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

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

Fix atom feeds and links

1. The atom feed for a group's issues didn't work, because it had parts copied from the dashboard issues builder template.
2. The feed link from a group's activity page went to the dashboard feed, rather than the group's feed.

Closes #15640

See merge request !4191

Fix broken link in CI quickstart docs

The newline between the `[label]` and the `(link)` caused it to be interpreted literally: http://doc.gitlab.com/ce/ci/quick_start/README.html

See merge request !3541

Improve issue formatting in Slack service

This will improve the looks of the message that gets send to Slack.

**Before**

![image](https://gitlab.com/jeroenvanbaarsen/gitlab-ce/uploads/670442d4d5cef5aa36753671b8894a75/image.png)

**After**

![image](https://gitlab.com/jeroenvanbaarsen/gitlab-ce/uploads/ab6e40a0c22ebe89ebd5b3652821c6dd/image.png)

There is one thing I'm not certain about, thats sending the logo with the payload. Because this means we need to host the GitLab logo somewhere public, and every time a payload from any GitLab instance is send, we use that logo url. This might overload the server, or drive the bandwidth bill through the roof.
This is something @sytses or @dzaporozhets have to decide about.

@stanhu, you told me you were the author of the original code, maybe you can review?

See merge request !1308

Fixed typo in zen.scss and corresponding views



See merge request !4045

Make it clearer that /licenses is the OS license templates endpoint

Following the discussion on https://gitlab.com/gitlab-org/gitlab-ce/commit/13804aba867d19009ca94d820aa7ec650a509f5a#note_4961954.

Corresponding EE MR: https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/407

See merge request !4188

Signed-off-by: Jeroen van Baarsen <jeroenvanbaarsen@gmail.com>

Clean up the images from GitLab CI

Closes #17568

See merge request !4163

Remove bottom margin for flash message on home page

### Flash Messages 
Remove `margin-bottom: 16px` from `.no-ssh-key-message` and `.project-limit-message`. 
This added an unnecessary margin between the notification and the content which was brought up in this issue #14797.

### Affected files:
    ./app/assets/javascripts/project.js.coffee:      $(@).parents('.no-ssh-key-message').remove()
    ./app/assets/stylesheets/pages/projects.scss:.no-ssh-key-message, .project-limit-message {
    ./app/views/shared/_no_ssh.html.haml:  .no-ssh-key-message.alert.alert-warning.hidden-xs
    ./app/assets/javascripts/user.js.coffee:    $('.hide-project-limit-message').on 'click', (e) ->
    ./app/assets/javascripts/user.js.coffee:      $(@).parents('.project-limit-message').remove()
    ./app/assets/stylesheets/pages/projects.scss:.no-ssh-key-message, .project-limit-message {
    ./app/views/shared/_project_limit.html.haml:  .project-limit-message.alert.alert-warning.hidden-xs
    ./app/views/shared/_project_limit.html.haml:      = link_to 'Remind later', '#', class: 'hide-project-limit-message alert-link'

### Screenshots:
#### Before: 
![Screen_Shot_2016-05-16_at_11.45.17_PM](/uploads/35f9db16526830e49bc302e2d00ecf7e/Screen_Shot_2016-05-16_at_11.45.17_PM.png)

#### After:
![Screen_Shot_2016-05-16_at_11.38.24_PM](/uploads/b8f9ac29b574a99c962c52028f7e61dd/Screen_Shot_2016-05-16_at_11.38.24_PM.png)


See merge request !4173

[ci skip]
Signed-off-by: Rémy Coutable <remy@rymai.me>

Create import data in service and fix timing issues when scheduling job

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/17401

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/17376

See merge request !4106

This was using the user dashboard atom builder template, not one for the
group's issues.

Signed-off-by: Rémy Coutable <remy@rymai.me>

Fix api leaking notes when user is not authorized to read noteable

fixes #17302

See merge request !4102

fix typo making gitlab.com importing to fail

Fixes https://gitlab.com/gitlab-org/gitlab-ee/issues/565

See merge request !4181

Instrument all Grape API helpers

This has been added to help us figure out what's making certain Grape API calls slow (e.g. the one used for authorized keys as described in gitlab-com/operations#99).

See merge request !4169