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