Added dropdown to list all projects on project header
Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/4212
When clicking the current project name, it shows a dropdown menu with a list of all projects for that group or user.
When closed:
![Screen_Shot_2016-01-14_at_19.17.44](/uploads/a7258ba388dba238fc2f0468711fc729/Screen_Shot_2016-01-14_at_19.17.44.png)
When open:
![Screen_Shot_2016-01-14_at_19.17.51](/uploads/716533d9eb44b123c5fdff36a4740489/Screen_Shot_2016-01-14_at_19.17.51.png)
cc. @jschatz1
See merge request !2438