Add Create Merge Request buttons to commits page and push event.

Commits page:

![Screen_Shot_2015-05-09_at_22.27.09](https://gitlab.com/gitlab-org/gitlab-ce/uploads/f77c2e47f768b2fc132de6e3a2a0323e/Screen_Shot_2015-05-09_at_22.27.09.png)

Branches page:

![Screen_Shot_2015-05-09_at_22.55.24](https://gitlab.com/gitlab-org/gitlab-ce/uploads/b0a6374f5c5d830ef19de9694e603c8f/Screen_Shot_2015-05-09_at_22.55.24.png)

Push event: (Only for new branches, and only shown to the pushing user)

![Screen_Shot_2015-05-09_at_22.27.21](https://gitlab.com/gitlab-org/gitlab-ce/uploads/989c9cb66ee03d09b96809452749d2b8/Screen_Shot_2015-05-09_at_22.27.21.png)

Push event with multiple commits and a Compare link:

![Screen_Shot_2015-05-09_at_22.28.01](https://gitlab.com/gitlab-org/gitlab-ce/uploads/a70c718e559f69177f9341c0af92707c/Screen_Shot_2015-05-09_at_22.28.01.png)

See merge request !632