UI Improvement for the project page

This MR improves the positioning of the dropdown menu on the project page.
I've added the WIP because I didn't check if this can cause any tests to break.
I'll remove it once the CI is green.

Before:
![gitlab_dropdown_old](https://gitlab.com/haynes/gitlab-ce/uploads/ac30810abe9e75154edd2a896c9a4947/gitlab_dropdown_old.png)

After:
![gitlab_dropdown_new](https://gitlab.com/haynes/gitlab-ce/uploads/616c237fe26934ebbbc82f0ce73e72da/gitlab_dropdown_new.png)

This is the MR for the discussion in gitlab-org/gitlab-ce!971 .

/cc @dzaporozhets Can you review it please? 😃

See merge request !1199