Add checkboxes to the application settings page for restricted
visibility levels, and remove those settings from gitlab.yml.

Supports four different event types all bundled under the "note" event type:

- comments on a commit
- comments on an issue
- comments on a merge request
- comments on a code snippet

1) Adds a DB migration for all services to toggle on push, issue, and merge events.

2) Upon an issue or merge request event, fire service hooks.

3) Slack service supports custom messages for each of these events. Other services
not supported at the moment.

4) Label merge request hooks with their corresponding actions.

Closes #1932.

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

adding avatar to project settings page added avatar removal show project avatar on dashboard, projects page, project page added rspec and feature tests added project avatar from repository new default project icon added added copying af avatar to forking of project added generated icon fixed avatar fork hound fix style fix test fix

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