Resolves #9285

This reverts commit 5daf44b7, reversing
changes made to 2f706fbd.

This reverts commit 957e849f, reversing
changes made to 6b9dbe9f.
Signed-off-by: NDmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Add gitlab-shell to error message to give user a clue that something may be wrong there.

Ran into this in #2082. User was told that repositories were created when they were
not due to hooks symlink being wrong.

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

Now there is a single source of information for which attribute a model
uses to be referenced, and its special character.

This would result in a 404 error in certain views.

The `save` call was being rolled back due to an error in the validation step.
Relax the validation step so that this works.

Closes #1570

This reverts commit 548f1828.

Allow admins to use restricted visibility levels when creating or
updating projects.

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

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.

Irker is a gateway which sends IRC messages on git updates. This new
service provides an interface to this gateway, integrated in Gitlab, for
each updates.
As per the guidelines, this commit adds the new feature in the
CHANGELOG, tests and documentation.

See http://www.catb.org/esr/irker/

* Impl Project#avatar_url
* Refactor ApplicationHelper: Use Project#avatar_url
* Update changelog