Possible workaround for #15392

Optimistic locking for Issue and Merge Requests

## What does this MR do?

It implements Optimistic Locking http://api.rubyonrails.org/classes/ActiveRecord/Locking/Optimistic.html for Issues and MRs but in a bit custom way. We use it for cases when either title or description field is involved in the change.

## Why was this MR needed?

We have to prevent data losing.

## What are the relevant issue numbers?
https://gitlab.com/gitlab-org/gitlab-ce/issues/12940

## Screenshots (if relevant)

![Screen_Shot_2016-07-09_at_15.33.02](/uploads/2efbe547a12fda93bce347fa711438d7/Screen_Shot_2016-07-09_at_15.33.02.png)


See merge request !5146

Cache todos pending/done dashboard query counts

See #19273

See merge request !5175

Remove unused RelativeUrl spec support file

See merge request !5207

Bump gitlab-workhorse version for !5094

I think I've created this merge request shortly after I committed this, but it's missing now??

See merge request !5214

Fix GitHub client requests when rate limit is disabled

## What does this MR do?

GitHub Rate Limit API returns 404 when the rate limit is disabled. In this case we just want to return gracefully instead of spitting out an error.

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

No.

## Why was this MR needed?

GitHub importer fails when rate limit is disabled in GitHub Enterprise.

## What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ee/issues/697

## Does this MR meet the acceptance criteria?

- [X] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry 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)
- [ ] 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 !5191

ObjectRenderer uses read_multi to read cache

## What does this MR do?

Get cache rendered content in bulk

## What are the relevant issue numbers?

#19273

## 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 !5096

Remove the group avatar link.

## What does this MR do?
For group pages, e.g. https://gitlab.com/groups/gitlab-org, I see no reason to link to the avatar image itself when clicking on the avatar.

If the user really wants to open the image, they can do so by right clicking and opening the image in a new tab.

As mentioned in https://gitlab.com/gitlab-org/gitlab-ce/issues/12806#note_12976019.

cc: @fatihacet @alfredo1 

See merge request !5196

Prefer string for describe as of:

https://gitlab.com/gitlab-org/gitlab-ce/blob/b7ba5fa06bfb434c9227a2175f936fc31fd3444f/doc/development/gotchas.md#dont-describe-symbols

See merge request !5202

Refactor permissions.md

- Move `permissions/permissions.md` to `user/permissions.md`
- Remove wrong assumptions about group visibility
- Merge CI `ci/permissions/README.md` to `user/permissions.md`

## What are the relevant issue numbers?

Resolves https://gitlab.com/gitlab-org/gitlab-ce/issues/19414

See merge request !5210

For group pages, e.g. https://gitlab.com/groups/gitlab-org, I see no reason to link to the avatar image itself when clicking on the avatar.

If the user really wants to open the image, they can do so by right clicking and opening the image in a new tab.

Reset project pushes_since_gc when we enqueue the git gc call

## What does this MR do?

Reset counters just when we really enqueue the `git gc` command. So as this is part of the `#execute`method we throttle the enqueue and the reset (database statement) as we throttle the `#increment!` call. And we only call `#execute` if it's needed.

## What are the relevant issue numbers?

Closes #19711 

## 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 !5201

Rename profile navigation tab 'Personal Access Tokes' to 'Access Tokens'

For https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/3749#note_12994215. We should not use more than 2 words for tab name 

See merge request !5187

* upstream/master:
  Expire the branch cache after `git gc` runs
  Be explicit on merge request discussion variables
  Improve wording in UI guide
  Fix expandable diffs
  CHANGELOG was updated.
  Style of import project buttons were fixed in the new project page.
  api: expose {should,force}_remove_source_branch
  Fix typo in UI guide
  Add rule about adding new header tab to the ui guide
  Update the health_check gem to the latest release
  Display tooltip for "Copy to Clipboard" button (!5164)
  Remove icons from some buttons which already has text

Remove icons from some buttons which already has text

Related to https://gitlab.com/gitlab-org/gitlab-ce/issues/18324


* remove plus icon from new milestone button on group milestone page
* remove plus icon from new project button on group projects page
* remove plus icon from milestone page

See merge request !5050

Expire the branch cache after `git gc` runs

Due to a stale NFS cache, it's possible that a branch lookup fails while `git gc` is running and causes missing branches in merge requests.

I'm not totally convinced this is the right solution, but since we and our customers are experiencing this issue quite frequently, I'm taking a stab at it.

Possible workaround for #15392


See merge request !5160

Be explicit on merge request discussion variables

## What does this MR do?

To avoid conditionals and to messing with request.format and accept headers to know in which format we're going to response I've decided to be explicit in when we need the discussion variables

## Why was this MR needed?

Solve a bug https://sentry.gitlap.com/gitlab/staginggitlabcom/issues/8492/

## What are the relevant issue numbers?

Closes #19702 

## 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 !5204

Style of import project buttons were fixed in the new project page.

## What does this MR do?
I have fixed style of import project buttons in the new project page.

## Are there points in the code the reviewer needs to double check?
I don't think so.

## Why was this MR needed?
Because the buttons area hasn't looked well. Before this, it was scattered.

## What are the relevant issue numbers?
Fixes #19467 

## Screenshots (if relevant)
![Screen_Shot_2016-07-11_at_17.12.11](/uploads/35918f16b1b4d671ad33faf6caf530a2/Screen_Shot_2016-07-11_at_17.12.11.png)
![Screen_Shot_2016-07-11_at_17.11.24](/uploads/3030e1ecb7d109fbf4552987b4bfb242/Screen_Shot_2016-07-11_at_17.11.24.png)
![Screen_Shot_2016-07-11_at_17.11.50](/uploads/eb8ede86c256a2356b0210f3876c0143/Screen_Shot_2016-07-11_at_17.11.50.png)

## 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 !5183

Due to a stale NFS cache, it's possible that a branch lookup fails
while `git gc` is running and causes missing branches in merge requests.

Possible workaround for #15392

Fix expandable diffs

## What does this MR do?

Fix expandable diffs and the master build.

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

Nope.

## Why was this MR needed?

https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/4776#note_13003494

Doesn't need a CHANGELOG entry etc.

See merge request !5200

Add rule about adding new header tab to the ui guide

To address cases like https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/3749#note_12994215 

See merge request !5188