CI: Add 'triggers' keyword to 'only' and 'except' lists to allow control over when triggers cause builds to run

Currently, the `only` and `except` keywords in `.gitlab-ci.yml` only accept ref names or the special `branches` and `tags` keywords. However, these are primarily useful when controlling how repository activity affects the creation of builds. In my case, instead of building on every commit, I'd like to use the following logic:

- If the repository is tagged, do a build.
- Any other normal commits should not cause a build.
- If a build is triggered via the API, always create one for the specified ref.

From what I can tell, this isn't possible via the existing YAML syntax. In this MR, I introduce a new keyword `triggers` that goes along with `branches` and `tags`. I can implement the logic above using the following job configuration:

```yaml
only:
  - tags
  - triggers
```

I updated the tests and documentation to reflect this and everything seems to pass.

See merge request !3230

Fix Indentation lints in CSS.

As discussed in #14299.

cc: @jschatz1 

See merge request !3312

Remove duplicated ago

Closes #14460 

See merge request !3332

Changing project icon

Closes #14196

See merge request !3268

Follow the CSS Style Guide rules for using shorthand where possible.

Fixes violations of the Shorthand rule. All of these were done manually and I reviewed each change to verify, so they should all be right.

Discussed in #14299.

cc: @jschatz1 

See merge request !3313

Check if index exists before adding it

I got an error when updating GDK because it already exists.

[ci skip]

See merge request !3335

Add group visibility level

Supersedes https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/3051

Closes #12658

See merge request !3323

Fix diff image view modes (2-up, swipe, onion skin) not working

Example test case: https://gitlab.com/mrtzcspr/test/commit/5d983226b1308d98ef3d8919b978ad49f34496b8

Closes #13856

See merge request !3316

Use gitlab-workhorse 0.7.1

A small extra defense against interrupted git raw responses. Nice to
have in 8.6 because we introduce /raw/ caching; it would be
unfortunate if incorrect (truncated) responses got cached.

See merge request !3330

Improve performance of viewing individual issues

This MR does two things:

1. `Issue#related_branches` no longer performs Git operations that aren't needed
2. The output of `Repository#exists?` is now cached and flushed properly

Combined these two changes should further cut down the amount of Git operations performed when viewing individual issues (and possibly other pages).

See merge request !3296

Ability to move issue to another project

Tasks:

- [x] Create scaffold of service that will move issue to another project.
- [x] Close old issue, add system note about moving issue to a new project.
- [x] Create a new issue, add system note about issue being moved from old project.
- [x] Check if issue can be moved to another project before executing service
- [x] Check permissions when moving an issue (`:admin_issue` ability)
- [x] Display select box for a new project when editing an issue
- [x] Show only projects that issue can be moved into in that select box
- [x] Add project select handler, helper and some permission filters to it
- [x] Preserve as much information as possible, including author
- [x] Prepare mechanisms that unfolds local references in issue description
- [x] Rewrite issue description with references unfolding and add some specs for it
- [x] Rewrite all system notes and comments attached to issue that is being moved
- [x] Update `Label` so that is was able to create cross reference labels (separate MR)
- [x] Add notifications about moving issue to another project
- [x] Display confirmation alert/message when issue move has been requested
- [x] Make it possible to undo selecting project where issue will be moved to
- [x] Add column to issue, that will indicate if it has been moved to another project
- [x] Do not allow to move issue that has been already moved
- [x] Write top-to-bottom feature spec in RSpec instead of Spinach

UI:

![issue_move_ui](/uploads/b3c6b563362c1fded9082cc0f51e5a74/issue_move_ui.png)

![issue_move_tooltip](/uploads/2ab913b06f52df1cafde9abe89bd9cb8/issue_move_tooltip.png)

Closes #3024

See merge request !2831

Do not retry "git gc"

To prevent 'git gc' timing out on a large repo and then bouncing
around in the retry queue.

See merge request !3266

attempting to fix omniauth problem

Attempt to fix https://gitlab.com/gitlab-org/gitlab-ce/issues/3361

See merge request !2876

Fix a few remaining uses of `0px`.

See #14299 for more information.

cc: @jschatz1 

See merge request !3310

Fix bug where wrong commit ID was being used in a merge request diff to show old image

Closes #3769

Closes #14327

See merge request !3300

Easily (un)mark merge request as WIP using link

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/3768 and https://gitlab.com/gitlab-org/gitlab-ce/issues/3516

## Link to add `WIP` prefix (underline is visible because of hover)
![wipless_title](/uploads/72a6f7119ba9d8043ca8329641e97c3b/wipless_title.png)

## Link to remove `WIP` prefix
![wip_title](/uploads/8620ad65da9ef620b180603520fead55/wip_title.png)

## System note after WIP is added
![wip_sysnote](/uploads/2de073b75e854d2c9e243eb8b5d5c259/wip_sysnote.png)

## Widget with link to remove WIP
![wip_widget](/uploads/cf83ea93743c4c26d9df759c17cb9d7b/wip_widget.png)

## Flash after WIP is removed
![wip_flash](/uploads/27b7240cd5d7ceeb8b7b477abd94d7ff/wip_flash.png)

## System note after WIP is removed
![wipless_sysnote](/uploads/c0d3368abdf21a2f253532a9a9594d90/wipless_sysnote.png)

## Widget when current user cannot remove the WIP prefix
![wip_widget_unauthorized](/uploads/174ccf1674be86dc81c3078fe297acb7/wip_widget_unauthorized.png)

cc @creamzy 

See merge request !3006

Backport premailer and diff changes from EE

Backport part of https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/151

See merge request !3318

Expand the issuable sidebar when coming back from the Changes tab

Unless the user explicitly requested the collapsed sidebar.

Fixes: #14353

See merge request !3256

#to_branch_name now uses the iid as postfix

Given the branch name 'mep-mep' with an iid being 1,
the current way, master's way, would yield a branch name of
1-mep-mep. The problem for larger projects however would be that
a developer might forget what iid the issue was.

When this developer would try to tab complete it would:
- Or result in 20+ branches possibly
- Or start with the wrong digit, try again with digit++
  - Would see 20 branches, repeat

Thus the obvious way of solving this is letting the dev tab complete
on the issue title, which is easier to remember.

@DouweM Should this be labelled `pick-in-master`? 

See merge request !3308

Dedupe labels in labels selector in Dashboard pages

Fixes #14418.

See merge request !3311

Fix spacing below edit note form

Also changed to allow the CSS to decide what should be hidden when editing

Thanks @JobV for having eagle eyes 😜 

See merge request !3306

Fixed issue with filtered data persisting when dropdown closed

![labels](/uploads/4b9c902add76263d8488cc34ef49f142/labels.gif)

Closes #14401

See merge request !3302

Add label description in tooltip to labels in issue index and sidebar

The tooltip can get quite big, but it’s so useful to inform people about what these labels mean
new

![Screen_Shot_2016-03-08_at_11.48.28](/uploads/894baaaa1f789c3a2069a924d541e64b/Screen_Shot_2016-03-08_at_11.48.28.png)

![Screen_Shot_2016-03-08_at_11.48.20](/uploads/efe4fa0960054c4071b8f6bf83024403/Screen_Shot_2016-03-08_at_11.48.20.png)

@JobV writes on Slack:
> yeah I think it’s better than not, but I’d have to try it 😃 
> 
> cautious yes, revert if it’s annoying 😉

See merge request !3124

Add information about `image` and `services` field at `job` level in the `.gitlab-ci.yml` documentation

Fixes #14366

/cc @tmaczukin @ayufan @axil

See merge request !3277

Trigger a todo for mentions on commits page

Closes #14006 

* Screenshot:

![todo-commit](/uploads/5d34de0b7afcea7548123dafddf60c45/todo-commit.png)

See merge request !3262

Adds small AJAX optimistic functionality to todos.

Fixes #13656 <br/>
A good first step and boring solution. <br/>
Will make ajax call to remove each issue.  <br/>
If issue is last in group of issues will refresh page.  <br/>
If issues remain in group will remove row with JS.  <br/>
Adds loading spinner to button and disables. <br/>

![todos-optimistic](/uploads/c6aec4a688e5125d4df55a2a3a55d4d7/todos-optimistic.gif) <br/>

cc @dzaporozhets @JobV @dbalexandre 

See merge request !2946

Fix an issue when the target branch of a MR had been deleted

Before displaying the "diverged commits" note, we're checking if the MR
is open, but we should check if it's mergeable instead because this
check ensure the source and target branches exist.

This was introduced by !2217 and fixes #14388.

See merge request !3294

Fix MergeRequest#source_sha when there is no diff

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/14170

### Overview

This MR fixes an unhandled Exception when visiting the page of an open Merge Request  without diff.

### Description

`MergeRequest#source_sha` is expected to return the sha of the source branch last commit. But when an open Merge Request has no diff (e.g. all commits have already been merged to the target branch), `merge_request.source_sha` incorrectly returns `nil`.

This was without consequences before – but since !2217 was merged (a few days ago), it makes `Gitlab::Git::Commit.between` raise an "Unexpected nil argument" exception. This can be reproduced when visiting the http://localhost:3000/gitlab-org/gitlab-test/merge_requests/2 page on a fresh local Gitlab setup.

This MR fixes the crash, by making sure that `source_sha` returns a
correct result even when there is no diff available. I also added tests.

@DouweM I believe you wrote most of this code in the first place ; does this looks correct to you, or is there a better way to resolve this issue maybe?

See merge request !3135

Removed diverging commit count calculation from Repository#build_cache

Using a repository with 1000 branches the old `Repository#build_cache` method would take around 180 seconds to complete. Without calculating the diverging commit counts this method "only" takes around 60 seconds. 

See commit 28cc2413eb5ddf920ce0b5eed803121f8b884754 for more details. This fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/14058

cc @rspeicher 

See merge request !3274

Add avatar to issue and MR pages header

closes #14395
# For Issues

### Before
![Screen_Shot_2016-03-18_at_4.27.25_PM](/uploads/b097c8e304c9737e2f46ee25667829bf/Screen_Shot_2016-03-18_at_4.27.25_PM.png)

### After
![Screen_Shot_2016-03-18_at_4.22.10_PM](/uploads/f7d2b12c9455950c2e660b33e27c1827/Screen_Shot_2016-03-18_at_4.22.10_PM.png)

# For Merge Request

### Before
![Screen_Shot_2016-03-18_at_4.27.09_PM](/uploads/50c7b6ee346f749f448647004ae6031b/Screen_Shot_2016-03-18_at_4.27.09_PM.png)

### After
![Screen_Shot_2016-03-18_at_4.24.17_PM](/uploads/abd37ccf030e0b6d10521a6937206de6/Screen_Shot_2016-03-18_at_4.24.17_PM.png)

See merge request !3301

Fixes issue with any milestone value in dropdown not being selectable

Closes #14293

See merge request !3234

Fixes issue with filter label missing on labels & milestones

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/14407

See merge request !3297

Changing filter dropdowns shows loading

Instead of doing a full refresh of the page - i've modified the filterResults method on the Issues object to work for this form as well

![issues](/uploads/3335f09f7df88b6d419de7fd3d6857d2/issues.gif)

Closes #14359

See merge request !3237

Add confidential issues

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/3678

More information: https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/227

See merge request !3282

Prevent a 500 when a repository's root_ref is nil

Closes #14259

See merge request !3278

Improved issue sidebar

Updated the spacing throughout the sidebar so that it fits better on smaller screens. Also adds a more participants button to show any other participants after the first row.

Closes #13353

See merge request !3097

Dashboard labels

Previously because there were no JSON endpoint for labels or milestones
it was fetching HTML and parsing that. This is wrong.

It now fetches from a JSON endpoint.

This also fixes the dashboard/issues page not loading labels or
milestones as the path used to be only for a single project. So instead
I have created a endpoint for labels & milestones JSON on dashboard.

See merge request !3253

Fixes issue with close button not working on MR

Closes #14383

See merge request !3295

Add note in upgrade guide to choose the correct version tag

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/3448

@rspeicher I'm assigning to you since as a release manager you should know better. Let's keep it in this guide for now and then start copying it in the future ones.

See merge request !2284