Move abilities by subject class to a dedicated method (EE)

## What does this MR do?

Twin of gitlab-org/gitlab-ce!5668.

It moves the `case` that returns abilities depending on the subject class to a dedicated method.

This should avoid lame conflicts when CE to EE since the EE version assign the result of the `case` to a variable.

## What are the relevant issue numbers?

Closes gitlab-org/gitlab-ce#20621.

See merge request !622

Signed-off-by: Rémy Coutable <remy@rymai.me>

This will avoid lame conflicts when merging CE to EE
Signed-off-by: Rémy Coutable <remy@rymai.me>

Refactor build artifacts documentation

- Split user and admin documentation
- Use new location paths
- Add new Continuous Integration guide for the Admin area
- Link to new guide from the Admin area

CE MR https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/5662

See merge request !619

- Split user and admin documentation
- Use new location paths
- Add new Continuous Integration guide for the Admin area
- Link to new guide from the Admin area

Fix assigning merge request to a project approver

Scope the options of a user select, so the data attributes of a user select 
are respected within its scope

Fixes #836.

See merge request !604

CE to EE for 8.11.0-rc1

See merge request !607

Use raw_diffs for internal git diff

With the merge of https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/5401 into EE, we need to update the usage of diffs, and instead use raw_diffs which is the previous behaviour.

See merge request !617

change the API on the merge_request_diff model from diffs -> raw_diffs

## What does this MR do?

Unify diffs API

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

## Why was this MR needed?

## What are the relevant issue numbers?

## Screenshots (if relevant)

## 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
- [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 !5650

See https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/5401

Speed up methods that depend on diff stats only

## What does this MR do?
Speeds up and reduces memory usage of `Commit#repo_changes`loop, `Repository#expire_avatar_cache` and `IrkerWorker`.  It's a WIP because it need a new version of `gitlab_git` released with [these changes](https://gitlab.com/gitlab-org/gitlab_git/merge_requests/109).

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

## Why was this MR needed?
For large files committed, this method ends up loading them in memory which can consume lots of memory.

## What are the relevant issue numbers?
https://gitlab.com/gitlab-org/gitlab-ce/issues/19441#note_13425892

## Screenshots (if relevant)
N/A

## 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~~
- [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 !5568

Update the gitlab-shell version in the tmp/tests directory to the right version

Previously the gitlab-shell version would never be updated if the directory existed via the `gitlab:shell:install` Rake task. This could lead to incompatibility issues or random errors.

See merge request !5646

Previously the gitlab-shell version would never be updated if the directory
existed via the `gitlab:shell:install` Rake task. This could lead to
incompatibility issues or random errors.

Cache diff syntax highlighted output

## What does this MR do?

Cache highlighted diffs for merge requests when they are requested for existing merge requests but after each change on the merge request diff recalculate again the cache.

I've introduced the concept of SafeDiffs which are the diffs that we're going to show on the UI and will be highlighted so maybe we can extend cache capabilities to more diffs.

The more problematic part is what and how we cache the highlighted lines, for the moment what I did was store in Redis as Gitlab::Diff::Line serialized as an array of json objects, similar of what we do for commits and diffs on merge request diffs.

The next step can be add a new field in the merge_request_diff object if we find it worth it. But let's first confirm this is the way to go

## What are the relevant issue numbers?

Closes #20034

## 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
  - [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 !5401

Hide SSH repository mirroring

## What does this MR do?
Removes reference to `ssh://` URLs from the repository mirror settings page

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

- [ ] Is the screenshot now used in the documentation an appropriate resolution?
- [ ] Do the remaining screenshots need re-doing to match?

Repository mirroring is also referenced from the 'Import project by URL' functionality, where much of the text of `_instructions.html.haml` is duplicated in a separate partial. It doesn't mention `ssh://`, though.

## Why was this MR needed?

Mirroring repositories over SSH needs more work before it's generally useful.

Currently, these URLs are interpreted with the implicit context of the SSH client configuration for the GitLab installation's `git` user, particularly `known_hosts` and any SSH private keys it has access to. Unless the user manually alters these details  - especially `known_hosts` - then `ssh://` URLs just don't work. 

We don't wish to support and document manual SSH configuration management, and the naive approach (a single `id_rsa` file used when mirroring all repositories) is insecure - especially for GitLab.com or similar deployments.

Future MRs will re-add documentation for `ssh://` URLs for both password and public-key authentication once `known_hosts` and unique SSH keys for repository mirroring are handled automatically.

Disabling support for `ssh://` URLs entirely would break existing customer setups.

## What are the relevant issue numbers?

#98 #621

## Screenshots (if relevant)

![Screen_Shot_2016-08-02_at_10.58.23](/uploads/940bce89b6e8cc109f5df766cd287c7d/Screen_Shot_2016-08-02_at_10.58.23.png)

See merge request !608

Add advanced troubleshooting for debugging issues with the Docker registry



See merge request !5615

[ci skip]

Use a full-width, HiDPI screenshot of repository mirroring to more closely match existing screenshots

Fix filter input alignment

## What does this MR do?
If you carefully observe the filter inputs on the [issues page](https://gitlab.com/gitlab-org/gitlab-ce/issues) and the [projects dashboard page](https://gitlab.com/dashboard/projects), you will notice that those input fields are actually a few pixels lower than the UI elements beside them (More so for the projects dashboard page than the issues page). This MR fixes that alignment issue so that they are aligned to the buttons on their right.

## Are there points in the code the reviewer needs to double check?
Shouldn't be

## Why was this MR needed?
Improves the existing UI

## What are the relevant issue numbers?
Closes #20559 

## Screenshots (if relevant)
Before
![Screen_Shot_2016-08-02_at_5.42.28_PM](/uploads/8530fc6c9ce20f28ae74b950bc1bd6be/Screen_Shot_2016-08-02_at_5.42.28_PM.png)

After
![Screen_Shot_2016-08-02_at_5.49.28_PM](/uploads/ec20e68045c2190aec52e5f059d1a3bc/Screen_Shot_2016-08-02_at_5.49.28_PM.png)

After (with color markings)
![Screen_Shot_2016-08-02_at_5.49.25_PM](/uploads/6e032b1ffb438018f6fadf294c3cebd3/Screen_Shot_2016-08-02_at_5.49.25_PM.png)

Before
![Screen_Shot_2016-08-02_at_5.41.19_PM](/uploads/11a3c30d0290328bb3298bc392facf9f/Screen_Shot_2016-08-02_at_5.41.19_PM.png)

After
![Screen_Shot_2016-08-02_at_5.49.47_PM](/uploads/f8e20346a19dc67cc3e54788dc0e72fb/Screen_Shot_2016-08-02_at_5.49.47_PM.png)

After (with color markings)
![Screen_Shot_2016-08-02_at_5.49.58_PM](/uploads/1839d5681ab2f3518609004511af86a6/Screen_Shot_2016-08-02_at_5.49.58_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 !5633

Move markdown doc to the right location



See merge request !612

[ci skip]

Move markdown doc to the right location



See merge request !5635

[ci skip]

So we have raw_diffs too

This object will manage Gitlab::Git::Compare instances

Instead calling diff_collection.count use diff_collection.size which is cache on the diff_collection

Introducing the concept of SafeDiffs which relates 
diffs with UI highlighting.

Remove delay when hitting Reply... button on page with a lot of comments

Every time the "Reply..." button was hit, a new `GLForm` was instantiated (which is fine), which would then call `GitLab.GfmAutoComplete.setup()` without specifying which textarea we needed autocompletion on, which resulted in `GitLab.GfmAutoComplete.setup` iterating through every single textarea on the page. On a page with a lot of comments, where each comment would have its own textarea that will be used to edit the comment, this would take a long time and cause the whole page to hang for 2 seconds when a  "Reply..." button was clicked.

See merge request !5602

Convert image diff background image to CSS

## What does this MR do?
Replaces the `trans_bg.gif` image used for image diff background image with a CSS implementation of the same background image

## Are there points in the code the reviewer needs to double check?
None

## Why was this MR needed?
Uses CSS to replace the use of an image so that webpage rendering is slightly improved

## What are the relevant issue numbers?
Closes #20500 

## Screenshots (if relevant)
Before:
![Screen_Shot_2016-08-01_at_12.29.10_PM](/uploads/8269877c561c29e6b0ca988079ff3fc6/Screen_Shot_2016-08-01_at_12.29.10_PM.png)

After:
![Screen_Shot_2016-08-01_at_12.29.16_PM](/uploads/cc88848b9c0e044445d19b889fd79271/Screen_Shot_2016-08-01_at_12.29.16_PM.png)

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [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 !5598

Fix EE code after gitlab_git update from CE

Closes #842

See merge request !610