Implement Build Artifacts

This implements #3028 

1. It stores artifacts in shared/artifacts,
1. It adds `artifacts` to `.gitlab-ci.yml`,
1. We use GitLab Workhorse to offload artifacts uploading,
1. To download artifacts it uses GitLab Workhorse X-Sendfile extension,
1. There's one "artifact" per-build. The new upload removes previous one and creates a new one,
1. Default max artifact size is set to 100MB - this can be changed in settings.

Missing things:
1. Support for `.gitlab-ci.yml`: `artifacts: true or git-ls-files` which will upload all non tracked files,
1. Artifacts passing between builds.

GitLab Workhorse changes: https://gitlab.com/gitlab-org/gitlab-workhorse/merge_requests/5
GitLab Runner changes: https://gitlab.com/gitlab-org/gitlab-ci-multi-runner/merge_requests/46

Syntax:
```
artifacts:
  untracked: true # default: false
  paths: # default: empty
  - bin/files
```


See merge request !1584

Send build name and stage in CI notification e-mail



See merge request !1776

Add allow_failure field to commit status API

Closes #3196

See merge request !1685

[ci skip]

Fix duplicate entry for 8.1.0 release

Fix Drone CI service template not saving properly

This fixes an Error 500 when attempting to save a Drone CI template in the service template page. `hook.url` was not being used and depended upon a project when none existed.

/cc: @bugagazavr

Closes #3419

See merge request !1774

Closes #3419

Remove text-rendering property

Continues !1779

Closes #3220

[ci skip]

See merge request !1784

Closes #3220

[ci skip]

Replace CoffeeScript block into JavaScript in Views.

Remove CSS property preventing hard tabs from rendering in Chromium 45

This is to workaround a bug in Chromium 45 (https://code.google.com/p/chromium/issues/detail?id=446434),
which is the default browser in Ubuntu 14.04 and older.

Closes #3220

See merge request !1779

Remove duplicate CHANGELOG etnries

[ci skip]

See merge request !1782

[ci skip]

Bump rugged version to be in line with gitlab_git requirements



See merge request !1780

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

This is to workaround a bug in Chromium 45 (https://code.google.com/p/chromium/issues/detail?id=446434),
which is the default browser in Ubuntu 14.04 and older.

Closes #3220

Display target branch on MR list when it is different from project's default

Fixes #3072

The screenshot below shows both previous and current UI state:

![branch-mr-both](/uploads/5c1f0519e42bae4655f3eee37edfc356/branch-mr-both.png)

First merge request has default branch as a target, second one has non default branch as target.

See merge request !1741

Switch to state_machines-activerecord (Fixes: #3374)

state_machine is unmaintained

See merge request !1764

- Offloads uploading to GitLab Workhorse
- Use /authorize request for fast uploading
- Added backup recipes for artifacts
- Support download acceleration using X-Sendfile

For example view: shared/issuable/_context

CoffeeScript: 190ms
JavaScript: 19.7ms

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

* fix commit duration graph
* make graphs responsive
* fix wrong padding
* add a bit of explanation to colors
Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Fix duplicate entry for 8.1.0 release and remove unreleased tag.

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Change documentation of converting a MySQL-Database to a Postgres one

The instructions were missleading. See -> https://gitlab.com/gitlab-org/gitlab-ce/issues/2904

closes #2904

See merge request !1549

[ci skip]

[ci skip]