Build related UI fixes
## Before

## After

See merge request !2015
Fix problems with award-emoji-only comment
This fixes a conflict between note with only a single emoji in content
and award-emojis mechanisms.
Closes#3734
cc @vsizov
See merge request !1936
If a Web hook test fails due to an SSL error or some other error, report
the result back to the user instead of an Error 500.
Closes#3656
Handle response
Award Emoji
This it first iteration of award emoji feature.
We have plan to extend emoji picker by the next release.
For now, you can add award by clicking to the emoji picker or posting a regular comment with emoji like "👍" and any other. You can post not only emoji that listed in the emoji picker.
See merge request !1825
Prevent the last owner of a group from being able to delete themselves
by 'adding' themselves as a master
Replaces !1708.
Fixes#1111.
See merge request !1815
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
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:

First merge request has default branch as a target, second one has non default branch as target.
See merge request !1741
- Offloads uploading to GitLab Workhorse
- Use /authorize request for fast uploading
- Added backup recipes for artifacts
- Support download acceleration using X-Sendfile