Optimize branch lookups and force a repository reload for Repository#find_branch

See merge request !6087

Some minor updates to upgrade guides for 8.12.

See merge request !6154

Resolve "Inconsistency: Repo Title "down caret" cropped on smaller viewports"

## What does this MR do?

Fixes an issue where the dropdown chevron for a project list was not visible on smaller viewports.

This MR also changes the dropdown trigger into a `button` element for better accessibility (it can now be tabbed to like any link).

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

None that I can think of.

## Why was this MR needed?

Better accessibility and support for smaller viewports.

## Screenshots (if relevant)

Dropdown toggle now targetable by pressing tab to select.
![Screen_Shot_2016-08-31_at_9.12.15_PM](/uploads/8b2038a8ae259efd32da2e94a309ce88/Screen_Shot_2016-08-31_at_9.12.15_PM.png)

Chevron no longer hidden when project title length triggers `overflow: ellipsis`.
![Screen_Shot_2016-08-31_at_9.13.38_PM](/uploads/382e76c06e54bc307106a84ec21ab892/Screen_Shot_2016-08-31_at_9.13.38_PM.png)

## Does this MR meet the acceptance criteria?

- [x] 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)

## What are the relevant issue numbers?

Closes #21506

See merge request !6140

Replace play icon font with svg

## What does this MR do?
Replaces the `play` font awesome icon with svg

## Are there points in the code the reviewer needs to double check?
Make sure that the svg is looking great on all the changed pages

## Why was this MR needed?
SVG is better than fonts 😄 

## What are the relevant issue numbers?
 #21455 

## Screenshots (if relevant)
Before (Pipeline):
![Screen_Shot_2016-08-26_at_4.16.16_PM](/uploads/90a75b91b516e643f2134e053b0d7590/Screen_Shot_2016-08-26_at_4.16.16_PM.png)

After (Pipeline):
![Screen_Shot_2016-08-26_at_4.15.49_PM](/uploads/44e44a3d4c14066b8b7ec8c3da36e012/Screen_Shot_2016-08-26_at_4.15.49_PM.png)

Before (Environments):
![Screen_Shot_2016-08-31_at_3.03.35_PM](/uploads/bd4087a9f01c1a4d3c373d2662df4fe5/Screen_Shot_2016-08-31_at_3.03.35_PM.png)

After (Environments):
![Screen_Shot_2016-08-31_at_3.00.23_PM](/uploads/0ec45031bedb271f16bea3544cbfe52b/Screen_Shot_2016-08-31_at_3.00.23_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 !6038

Center build stage columns in pipeline overview

## What does this MR do?
Centers the build stage table content and headers in the [pipeline view](https://gitlab.com/gitlab-org/gitlab-ce/pipelines)

## Are there points in the code the reviewer needs to double check?
Need to check whether it is okay to remove the following ([commit that added this property](https://gitlab.com/gitlab-org/gitlab-ce/commit/6130376ad6673facb729b78878f9156a29948a5b))
```
.light {
    width: 3px;
}
```

## Why was this MR needed?
Improve UI

## Screenshots (if relevant)
Before:
![Screen_Shot_2016-08-31_at_12.46.43_PM](/uploads/cc4973d2155b59b32ec6fde714fbc26d/Screen_Shot_2016-08-31_at_12.46.43_PM.png)

After:
![Screen_Shot_2016-08-31_at_12.46.28_PM](/uploads/561d7b3973398c827d88870b38136c7d/Screen_Shot_2016-08-31_at_12.46.28_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)

## What are the relevant issue numbers?
Closes #21708

See merge request !6135

Project tools visibility level

## part of #19734   

![project_features_access_level](/uploads/81ec7185d4e61d7578652020209af925/project_features_access_level.png)

## 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 !5606

Merge request sha info

## What does this MR do?

Exposes `sha` and `merge_commit_sha` items in `MergeRequest` API endpoint data.

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

No.

## Why was this MR needed?

It's useful information.

## What are the relevant issue numbers?

Closes #20456.

## 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
- [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 !5966

Use JavaScript tooltips for mentions

## What does this MR do?

- use JavaScript tooltips instead of plain title for mentions (issue, merge request, snippet, user, group, commit, commit range, milestone)

## Why was this MR needed?

JavaScript tooltips look nicer and can wrap.

## What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/5261#note_13106713, fixes #21500

See merge request !5301

Order award tooltips by their created_at date

## What are the relevant issue numbers?

Closes #20601

See merge request !6086

Fix suggested colors options for new labels in the admin area

## What does this MR do?

Execute the JS related to the suggested colors options when user access the new label in the admin area.

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

No.

## Why was this MR needed?

Clicking in a suggested color when creating a new label in the admin area don't change the background color.

## Screenshots (if relevant)

* Before

    ![2016-08-31_19.56.14](/uploads/3d50236dac578910c5062aa1e83da350/2016-08-31_19.56.14.gif)

* After

    ![2016-08-31_19.58.59](/uploads/376ffdcbb5b80ef51ab1d642fe9486d0/2016-08-31_19.58.59.gif)

## Does this MR meet the acceptance criteria?

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

## What are the relevant issue numbers?

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/21726

See merge request !6138

Expire commit view partial after a day

See merge request !6128

Add MR Documentation description template

Add an MR Documentation template for `gitlab-ce`.

See merge request !6145

If `git gc` runs and `Repository` has an instance to `Rugged::Repository`, a
bug in libgit2 may cause the instance to return a stale value or a missing
branch. This change not only optimizes the branch lookup so we don't have
to iterate through every branch, but it also works around the `git gc`
issue by forcing a repository reload every time `Repository#find_branch`
is called.

See: https://github.com/libgit2/libgit2/issues/1534

Closes #15392, #21470

Hide group control nav if no options present

## What does this MR do?

Hides the group nav controls if no options present in the dropdown.
Also fixed the alignment of the dropdown to match the project page.

## What are the relevant issue numbers?

Closes #19120 

See merge request !5155

GitHub importer use default project visibility for non-private projects

## What does this MR do?

GitHub importer use the `Default Project Visibility` setting for all non-private projects.

## Why was this MR needed?

This allow users to import projects when `Public` visibility is restricted.

## What are the relevant issue numbers?

Fixes #21437

See merge request !6023

Refactor ability.rb into Policies

## What does this MR do?
Factors out `ability.rb` into a new abstraction - the "policy" (stored in `app/policies`). A policy is a class named `#{class_name}Policy` (looked up automatically as needed) that implements `rules` as follows:

``` ruby
class ThingPolicy < BasePolicy
  def rules
    @user # this is a user to determine abilities for, optionally nil in the anonymous case
    @subject # this is the subject of the ability, guaranteed to be an instance of `Thing`
    can! :some_ability # grant the :some_ability permission
    cannot! :some_ability # ensure that :some_ability is not allowed. this overrides any `can!` that is called before or after
    delegate! @subject.other_thing # merge the abilities (can!) and prohibitions (cannot!) from `@subject.other_thing`
    can? :some_ability # test whether, so far, :some_ability is allowed
  end

  def anonymous_rules
    # optional. if not implemented `rules` is called where `@user` is nil. otherwise this method is called when `@user` is nil.
  end
end
```

See merge request !5796

Add a BroadcastMessage API

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/21628

See merge request !6112

Fix bug where pagination is still displayed despite all todos marked as done

## What does this MR do?
Changes the todo `mark all as done` button callback to remove pagination and add user friendly text `"You're all done!"` so that it is consistent with what the page should look like after refreshing

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

## Why was this MR needed?
Resolve existing UI inconsistency

## Screenshots (if relevant)
Before:
![8xDRiXB1TL](/uploads/479edbdedf8d468b4c5e502f36a0c19f/8xDRiXB1TL.gif)

After:
![q4XDxhujPX](/uploads/3566eb538e6ad5a2d32b78351b9bc47d/q4XDxhujPX.gif)

## 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)
- [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)

## What are the relevant issue numbers?
Closes #21048

See merge request !6113

Check for existance of elements under test in application_spec.js

## What does this MR do?

Checks that the elements under test in `application_spec.js` actually exist.

## Why was this MR needed?

```
$ echo 'just garbage' > spec/javascripts/fixtures/application.html.haml 
$ bundle exec teaspoon spec/javascripts/application_spec.js 
2 examples, 0 failures
```

See merge request !6051

Fixed escaping issue with labels filter

## What does this MR do?

Encodes label names to stop any JS errors.

## What are the relevant issue numbers?

Closes #15552

See merge request !6123

Remove redundant js-timeago-pending from user activity log

## What does this MR do?
Enables the `skip_js` feature of `time_ago_with_tooltip()` since the frontend was already re-initializing `timeago` on all the elements after it received the data from the backend.

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

## Why was this MR needed?

*  Reduces bandwidth usage (Reduced by ~3.1kb)
*  Removes redundant code
*  Happy DOM 🎈 

## What are the relevant issue numbers?
Closes #21063 

## Screenshots (if relevant)
Before (DOM):
![Screen_Shot_2016-08-18_at_11.14.18_AM](/uploads/8be02cff27e452670988db8ff54bd57c/Screen_Shot_2016-08-18_at_11.14.18_AM.png)

After (DOM):
![Screen_Shot_2016-08-18_at_11.26.51_AM](/uploads/a0c5cbcd4c7b8e524a848b50dbd88c55/Screen_Shot_2016-08-18_at_11.26.51_AM.png)

Before (Bandwidth):
![Screen_Shot_2016-08-18_at_11.28.24_AM](/uploads/c37de0b398d7c66770f1def1777ca11a/Screen_Shot_2016-08-18_at_11.28.24_AM.png)

After (Bandwidth):
![Screen_Shot_2016-08-18_at_11.29.49_AM](/uploads/dc21719b965df1e73c868470447a1b20/Screen_Shot_2016-08-18_at_11.29.49_AM.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 !5871

Filters tags by name

Closes #21673 

See merge request !6121

Fix sorting issues by "last updated" after import from GitHub

## What does this MR do?

Don't touch Issue/Merge Request when importing GitHub comments as it will trigger an update on `updated_at` field. It also use `updated_at` as the last updated date doesn't matter the Issue/Pull Request state.

## Why was this MR needed?

After import from GitHub, sorting issues by "last updated" doesn't work as expected.

## What are the relevant issue numbers?

Fixes #21567

See merge request !6110

Fix toggler_behavior.js to toggle ajax loaded contents like `diffs` page.

## What does this MR do?

Fix toggle in diffs

## What are the relevant issue numbers?

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/21676, https://gitlab.com/gitlab-org/gitlab-ce/issues/21686.

See merge request !6119