Add predefined CI variables to GitLab

## What does this MR do?
This adds predefined CI variables to GitLab for container registry, pipelines, project name, etc. It also makes sure that all currently documented variables are send from GitLab. This is added to follow up on this proposal: https://gitlab.com/gitlab-org/gitlab-ci-multi-runner/issues/185#note_11844286. To migrate almost all variables out of Runner to GitLab to simplify adding a new of variables without the need for changing the GitLab Runner.

## Why was this MR needed?
Our CI variables miss a lot of crucial information that should be easily accessible. This tries to fill this gap.

## What are the relevant issue numbers?
Fixes https://gitlab.com/gitlab-org/gitlab-ci-multi-runner/issues/185, https://gitlab.com/gitlab-org/gitlab-ce/issues/18164, https://gitlab.com/gitlab-org/gitlab-ce/issues/18075.

## Does this MR meet the acceptance criteria?

- [ ] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [ ] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [ ] API support added
- Tests
  - [ ] Added for this feature/bug
  - [ ] All builds are passing
- [ ] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [ ] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [ ] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)


See merge request !4826

Remove white background on clipboard button; position icon

## What does this MR do?
Removes white background from clipboard button

## What are the relevant issue numbers?
Closes #19098 

## Screenshots (if relevant)
![Screen_Shot_2016-07-18_at_3.12.24_PM](/uploads/4a6a540e1a074e6cf89fb99be1b49f2d/Screen_Shot_2016-07-18_at_3.12.24_PM.png)
![Screen_Shot_2016-07-18_at_8.50.55_PM](/uploads/8c594b6f9a74095b194fe1f634eaf226/Screen_Shot_2016-07-18_at_8.50.55_PM.png)

See merge request !5335

Fix build duration when build is not finished yet

## What does this MR do?

## Are there points in the code the reviewer needs to double check?

## Why was this MR needed?

## What are the relevant issue numbers?

Fixes #19937.

## Does this MR meet the acceptance criteria?

- [x] No CHANGELOG since it fixes a regression not yet in a stable release (I think)
- Tests
  - [x] Added for this feature/bug
  - [ ] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5323

speed up ExternalWikiService#get_project_wiki_path

## What does this MR do?

Speed up ExternalWikiHelper#get_project_wiki_path

## Are there points in the code the reviewer needs to double check?

## Why was this MR needed?

See issue #19886 

## What are the relevant issue numbers?

#19886 

## Screenshots (if relevant)

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [ ] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [ ] API support added
- Tests
  - [ ] Added for this feature/bug
  - [ ] All builds are passing
- [ ] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [ ] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [ ] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5305

Add new CI status icons

## What does this MR do?
Adds new CI status icons for every state

## What are the relevant issue numbers?
Closes #19847 

## Screenshots (if relevant)
![Screen_Shot_2016-07-19_at_6.58.37_AM](/uploads/ec391b59825f5a4a228d7c77e7485b1e/Screen_Shot_2016-07-19_at_6.58.37_AM.png)


See merge request !5280

New fork icon!

## What does this MR do?
We are using the old fork icon for branching only, so this implements our new custom fork icon

## Screenshots (if relevant)
![Screen_Shot_2016-07-15_at_9.22.33_AM](/uploads/05abaffff314e41f582189327bcca6b2/Screen_Shot_2016-07-15_at_9.22.33_AM.png)     
![Screen_Shot_2016-07-15_at_9.29.14_AM](/uploads/a08c622c92da00945406bbd4b3497749/Screen_Shot_2016-07-15_at_9.29.14_AM.png)

cc @hazelyang 

See merge request !5276

Replace namespace-specific application.js files with namespace-bundle.js files.

Following up on the per-page JavaScript improvements, I wanted to replace the use of `application.js` with `namespace-bundle.js` to prevent confusion when downloading more than one application.js file.

This is pretty much just for the sake of clarity.

cc: @alfredo1 

See merge request !5221

Allow to pull code with deploy key from public projects

## What does this MR do?
With deploy keys you can download any public projects stored in GitLab.

## What are the relevant issue numbers?
Fixes: https://gitlab.com/gitlab-org/gitlab-ce/issues/1217

## Does this MR meet the acceptance criteria?

- [ ] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [ ] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [ ] API support added
- Tests
  - [ ] Added for this feature/bug
  - [ ] All builds are passing
- [ ] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [ ] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [ ] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5316

Added redirect_to_referer to login link on issues

## What does this MR do?

Adds a `redirect_to_referer` param to login & register links on issues when not logged in. This makes the login box redirect back to the issue after login.

## What are the relevant issue numbers?

Closes #19968 

See merge request !5344

Simplify entities for branches and tags API

## What does this MR do?

As talked in !5208, I improved the entity for branches and tags.

## Does this MR meet the acceptance criteria?

~~- [ ] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added~~
~~- [ ] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)~~
~~- [ ] API support added~~
~~- Tests~~
  ~~- [ ] Added for this feature/bug~~
  ~~- [ ] All builds are passing~~
~~- [ ] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)~~
~~- [ ] Branch has no merge conflicts with `master` (if you do - rebase it please)~~
~~- [ ] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)~~

See merge request !5343

Use value of `yaml_variables` and `when` from config_processor if undefined

## What does this MR do?
Uses `yaml_variables` and `when` from config_processor if values for these are undefined.

## Why was this MR needed?
Old builds doesn't have this columns initialised. 
Thus makes the retries on these builds to not work properly.
This is regression introduced by https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/5296.

## Does this MR meet the acceptance criteria?

- Tests
  - [ ] Added for this feature/bug
  - [ ] All builds are passing
- [ ] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [ ] Branch has no merge conflicts with `master` (if you do - rebase it please)


See merge request !5342

Api delete todos

## What does this MR do?

It changes the `DELETE /todos` to only return the number of marked todos.

## Why was this MR needed?

Before it returned the marked todos as an paginated array. Since we deleted/marked the todos, there was no way to get the rest of the todos.

## What are the relevant issue numbers?

Closes #19678

## Does this MR meet the acceptance criteria?

~~- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added~~
- [x] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [x] API support added
- Tests
  - [x] Added for this feature/bug
  - [x] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5341

Added Rake task for tracking deployments

## What does this MR do?

This MR adds a Rake task to track the current version of GitLab in InfluxDB.

## Are there points in the code the reviewer needs to double check?

We may want to document this Rake task in some Markdown file, but I'm not sure what the best place for this would be.

## Why was this MR needed?

We want to have a more accurate overview of when deployments occurred. 

## What are the relevant issue numbers?

https://gitlab.com/gitlab-com/infrastructure/issues/98

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [x] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [x] ~~API support added~~
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [ ] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5320

Add support for manual CI actions

## What does this MR do?
This implements a `when: manual` which allows a jobs to be marked as manual actions.
Manual actions have to be explicitly executed by developers.

## What are the relevant issue numbers?
This is to solve: https://gitlab.com/gitlab-org/gitlab-ce/issues/17010

See merge request !5297

Project avatar import/export functionality

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/19851

Adds logic to export and import a project avatar

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- ~~[ ] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)~~
- Tests
  - [x] Added for this feature/bug
  - [x] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5273

Resolve "Add icons for branch and tag in pipeline list"

## What does this MR do?
Adds branch or tag icon on pipeline ref

## What are the relevant issue numbers?
Closes #19751    
Part of #18920 

## Screenshots (if relevant)
![Screen_Shot_2016-07-13_at_1.42.54_PM](/uploads/d90706a76cf87a6cc8c25dca9a71affa/Screen_Shot_2016-07-13_at_1.42.54_PM.png)

With icons closer to tag/branch name/sha:   
![Screen_Shot_2016-07-15_at_11.23.48_AM](/uploads/411338f811bafbd314dbab5553fa46d4/Screen_Shot_2016-07-15_at_11.23.48_AM.png)

See merge request !5239

Content Security Policy

Ref: #18231 

This uses twitter's [secure_headers gem](https://github.com/twitter/secureheaders).

See merge request !4770

Update MAINTENANCE.md with our latest policy

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/19958

See merge request !5339

Update documentation for build artifact dependencies

## What does this MR do?

Update documentation for build artifact dependencies

## Are there points in the code the reviewer needs to double check?

## Why was this MR needed?

#19892 

## What are the relevant issue numbers?

#19892 

## Screenshots (if relevant)


See merge request !5332

Blurs the clicked link in dropdown menus

## What does this MR do?

This fixes an issue where the dropdown menu would stay visible even when clicked out of it

See merge request !5322

Improve cron_jobs loading error messages

## What does this MR do?

Improves the error message from "Sidekiq Cron Jobs" plugin, when trying to load a incorrect definition from gitlab config files.

This is the output before the fix:

```
2016-06-08T16:43:19.277Z 2890 TID-gso49ojro INFO: Booting Sidekiq 4.1.2 with redis options {:url=>"unix:/var/run/redis/redis.sock", :namespace=>"resque:gitlab"}
undefined method `delete' for nil:NilClass
/home/git/gitlab/config/initializers/sidekiq.rb:16:in `block (2 levels) in <top (required)>'
/home/git/gitlab/config/initializers/sidekiq.rb:16:in `each'
/home/git/gitlab/config/initializers/sidekiq.rb:16:in `block in <top (required)>'
/home/git/gitlab/vendor/bundle/ruby/2.1.0/gems/sidekiq-4.1.2/lib/sidekiq.rb:70:in `configure_server'
```

This is the output after the fix:

```
2016-07-18T10:53:22.414Z 66332 TID-oxal1bmik INFO: Booting Sidekiq 4.1.4 with redis options {:url=>"redis://localhost:6378", :namespace=>"resque:gitlab"}
Invalid cron_jobs config key: 'registry'. Check your gitlab config file.
/home/git/gitlab/config/initializers/sidekiq.rb:21:in `block (2 levels) in <top (required)>'
/home/git/gitlab/config/initializers/sidekiq.rb:17:in `each'
/home/git/gitlab/config/initializers/sidekiq.rb:17:in `block in <top (required)>'
/home/git/gitlab/vendor/bundle/ruby/2.1.0/gems/ruby-2.1.8/gems/sidekiq-4.1.4/lib/sidekiq.rb:70:in `configure_server'
```

Fixes #18378

## Are there points in the code the reviewer needs to double check?

No

## Why was this MR needed?

Original error doesn't give any hint on where the problem can be, so the user can't easily troubleshoot unless he knows implementation details.

## What are the relevant issue numbers?

#18378

## Does this MR meet the acceptance criteria?

- [ ] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [ ] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [ ] API support added
- Tests
  - [ ] Added for this feature/bug
  - [ ] All builds are passing
- [ ] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [ ] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [ ] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5318

Don't blow up in tree view on empty repo

## What does this MR do?

Stop the empty repo page blowing up with a 500 error when a user's default view is tree view.

## Are there points in the code the reviewer needs to double check?

Don't think so.

## Why was this MR needed?

https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/4997 made sure that the `tree` filter was only called if the user's default project view is tree, but left out the empty repo check. When users visit an empty repo with the tree view as default, they now get a 500.

## What are the relevant issue numbers?

Closes #19928.

## Screenshots (if relevant)

## Does this MR meet the acceptance criteria?

- ~~[CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added~~ (bug introduced in same release)
- ~~[Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)~~
- ~~API support added~~
- Tests
  - ~~Added for this feature/bug~~
  - [ ] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)


See merge request !5317

Don't parse Rinku returned value to DocFragment when didn't change original html string.

See merge request !5311

Revert "Revert "Merge branch '18193-developers-can-merge' into 'master'""

## What does this MR do?

Reverts the revert of !4892 which lacked an EE MR at the time. This has been done in gitlab-org/gitlab-ee!564.

## What are the relevant issue numbers?

Closes #19872.

See merge request !5310

Fixed the alignment in the MR widget

## What does this MR do?

Fixes the alignment of the browse button in the MR widget

## Screenshots (if relevant)

![Screen_Shot_2016-07-17_at_17.47.54](/uploads/41dcb0fad38fdd4dbccfda5ffaeaec6e/Screen_Shot_2016-07-17_at_17.47.54.png)

See merge request !5307

Collapsed diffs lines/size don't accumulate to overflow diffs.

## What does this MR do?

Reduce the number of lines that we highlight on big diffs to try to reduce the degradation introduced by  !4990 as you can see on the issue description #19820 .

We collapse any files after the diff is over the number of safe files (100), or over the safe lines (500) or over the safe number of bytes (5KB x 100 files).

We still need to bump the gitlab_git and point this branch to the new gitlab_git version.

## What are the relevant issue numbers?

Closes #19820 
Closes #19885

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- ~~[ ] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)~~
- ~~[ ] API support added~~
- Tests
  - [x] Added for this feature/bug
  - [x] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)


See merge request !5306

Fix activity heatmap to show proper day name.

## What does this MR do?
This MR fixes issue #19909.

## Are there points in the code the reviewer needs to double check?
Not necessarily, it's pretty straightforward, buuuut

There was some discussion about whether GL wanted the activity heatmap to start on Monday or Sunday, this fix makes it start on Sunday, if GL is wanting it to start on Monday then some more substantial changes need to be made on the `calendar.js.coffee` script.

## Why was this MR needed?
The amount of day names that were off from their dates was too damn high! :P 

## What are the relevant issue numbers?
Directly #19909 

Also some related discussion (feature discussion):
#19282, #5988

## Screenshots (if relevant)
**Currently on GL.com**
![Screen_Shot_2016-07-16_at_10.56.02_PM](/uploads/b45cfc56c29a8865a2bdc1f798409706/Screen_Shot_2016-07-16_at_10.56.02_PM.png)

**After MR**
![Screen_Shot_2016-07-16_at_10.56.30_PM](/uploads/d8655bb259ced443a2c572ff03dcb8bb/Screen_Shot_2016-07-16_at_10.56.30_PM.png)

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- Tests
  - [x] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5303

Upgrade gemojione to 3.0.0

Upgrades gemojione to 3.0.0, see the Changelog: https://github.com/jonathanwiesel/gemojione/blob/b98aa8b07eef815d4d3f52ff3c8714b28932b0de/CHANGELOG.md#v300-2016-07-12

[Here are all the new 2016 emoji](http://emojione.com/releases/2.2.4/) 🎉

This update has new emoji and more sensical categories.

See merge request !5237

Allow build email service to be tested

Fixes #13343 

See merge request !5223

API: Expose 'developers_can_push' for branches

## What does this MR do?

Adds support for the `developers_can_push` flag for the branches API. It also supports creating protected branches with that flag.

## Are there points in the code the reviewer needs to double check?

The API call requires an optional boolean parameter `developers_can_push`. If it is not either `true` or `false`, it should not update the value. I'm not sure if this is the right way to do it.

Right now it always returns `200`. Maybe the `PUT` method should return different status codes depending if it really created or updated a branch.

## What are the relevant issue numbers?

Closes #12735 

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [x] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [x] API support added
- Tests
  - [x] Added for this feature/bug
  - [x] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5208

Render only commit title

## What does this MR do?
Render only commit title in builds



## Why was this MR needed?
Better readability

## What are the relevant issue numbers?
Closes #19420 

## Screenshots (if relevant)
![after](/uploads/fcdd59d74a0f91f6ac847f7f02d5f07f/after.png)![before](/uploads/71ca6dabf31452a1a8dfb15ecb8860c5/before.png)
## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added


- Tests

- [x] All builds are passing
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

cc: @kradydal @yorickpeterse @grzesiek @tmaczukin @dzaporozhets [@tomash](https://github.com/tomash) [@chastell](https://github.com/chastell)

this is connected to closed MR [!5109](https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/5109)

See merge request !5131

Fix MR diff encoding issues exporting projects

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/19338

See merge request !5039

Disable transaction when adding index for Ci::Pipeline

## What does this MR do?
Adds missing `disable_ddl_transaction!`

## Why was this MR needed?
Fixes a broken migration for PostgreSQL


See merge request !5319

Store when and yaml variables in builds table

## What does this MR do?
Stores `when` and `yaml_variables` in `ci_builds` table.

## Why was this MR needed?
This is done in order to simplify the code responsible for creating a pipeline builds.

## What are the relevant issue numbers?
This made as a pre-step for https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/5295.

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [x] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [x] API support added
- Tests
  - [x] Added for this feature/bug
  - [x] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [ ] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5296

Make docker registry work with location redirects when external storage is used

## What does this MR do?

Honor `Location:` header when working with local registry.
Location makes it possible to download manifests from external storage.

## What are the relevant issue numbers?

Fixed https://gitlab.com/gitlab-org/gitlab-ce/issues/18477

## Remark

Adding `FollowRedirects` makes that we leak `Authorization:` in followed requests.

That is why it is implemented manually and we are explicitly removing `Authorization` header.

cc @marin @twk3 

See merge request !4677