Fix CI permissions

![Screen_Shot_2015-09-21_at_20.23.16](https://gitlab.com/gitlab-org/gitlab-ce/uploads/6f40699507d0dce148d0054a093f0d63/Screen_Shot_2015-09-21_at_20.23.16.png)

This fixes two problems:
- Allow developers to retry builds
- Hide advanced project options from CI page for non-admin users



See merge request !1379

Fix Error 500 when comparing non-existing branches

Closes #2593

See merge request !1355

- Allow developers to retry builds
- Hide advanced project options from CI page for non-admin users

This will fix merge problem for merge requests between forks created
before 8.0

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

Notification levels can now be set on the Project's main page

![Screen_Shot_2015-09-16_at_7.49.49_PM](https://gitlab.com/gitlab-org/gitlab-ce/uploads/0ac517bdfdc801f0e2115463c3ea9e10/Screen_Shot_2015-09-16_at_7.49.49_PM.png)

The notification settings for a project can now be set directly on the Project's page. The drop down list and the button label reflect the current level.

Saving is done via a remote form submission and if successful shows the user a flash message:

![Screen_Shot_2015-09-16_at_6.09.02_PM](https://gitlab.com/gitlab-org/gitlab-ce/uploads/8a6e1fde5177aa3976cadf59fdb8d375/Screen_Shot_2015-09-16_at_6.09.02_PM.png)

@DouweM can you please review my code. I gave my bestest effort to make in clean and readable.

@rspeicher hopefully we can include it with the 8.0 release, maybe?

/cc @darby 

See merge request !1322

Addresses internal https://dev.gitlab.org/gitlab/gitlabhq/issues/2605

See https://github.com/tinfoil/devise-two-factor/pull/43

Closes #2593