Add container registry support
Tasks:
- [x] Merge docker/distribution authentication service: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/3787
- [x] Implement Docker Registry API
- [x] Show a list of docker images in GitLab
- [x] Remove registry repository on project deletion
- [x] Support project rename, move and namespace rename
- [x] Use token when connecting the registry
- [x] Allow to delete images from GitLab
- [x] Support pushing from GitLab CI (gitlab-ci-token / $CI_BUILD_TOKEN)
- [x] Support GitLab Runner pulling for public repositories
- [ ] Support GitLab Runner pulling for private repositories
- [x] Add tests for Docker Registry API
- [x] Add tests for a views
- [x] Make texts nicer
- [x] Implement a backup support
- [ ] Create administration documentation https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/4141
- [ ] Create user documentation
See merge request !4040
Update build log incrementally
Proof of concept implementation of incremental sending of build log to browser.
cc @jschatz1 @vsizov @grzesiek @tmaczukin
See merge request !3737
Reuse runners edit form in admin and project area
Reuse runners edit form in admin and project area.

See merge request !4094
Improve documentation and web test for web hooks
Tips and documentation of actual hook behavior. Improved user feedback
when testing hooks via the web UI.
See merge request !4015
We send a state of ansi2html to client, client needs to send this state back.
The state describes the configuration of generator and position within trace.
Backported minimal safewebhook implementation to GitLab CE
This brings a minimal implementation for gitlab-org/gitlab-ce#13478
backported from EE (gitlab-org/gitlab-ee!334).
Also added UI to configure Secret Token
Fixes#15365.
See merge request !3940
Load the "New Branch" button asynchronously
Here's how it looks like for logged in users:

And here it is for anonymous users (or when a new branch can't be created by a logged in user):

See merge request !3855