Re-enable notifying commit authors of new commit notes

* Show new merge request button from compare page
* Show message if user selected same branches
* Show message if compared branches are the same
* Prepend inputs with from/to labels

Trigger notification service when new user-group relation was created

Fix bug with rendering changing images in commits

Fix typo in tests

When viewing the diff for a changed image file, two bugs occur:

- Both the 'before' and 'after' images link to the 'after' commit
- Visiting the link for either image will cause a error

The first is caused by both image links referencing '@commit.id' rather
than '@commit.parent_id'.  The second is caused by the use of
'project_tree_path' which is used for creating links to directories in
the git file tree. 'project_blob_path' which links to files should be
used instead.

Update User api to respect default settings

Change-Id: Ia723321a5cb05deb626d34c7d8d78194e049b1f0

Change-Id: Ib4eb533dff5c722fe559330e4aa71b5d5baf6fb8

-calling build_user will now apply defaults and only override them if as: :admin is set

Change-Id: Id1d938c0967752ecc14370af54f2d88128d18c44

-API now respects default_projects_limit, default_can_create_group, and default_can_create_team

Change-Id: I059d060d576df1050e5371e707381c5e8c608a7a

Fix user.several_namespaces? to work with multiple ownership of groups

Add link to project page from admin view

-i flag allows sudo to work for git users using rvm that is not being us...