Step 1:
* Add milestone_id in the model for merge_requests
* Make it possible to create or update a Merge Request with an attached
  Milestone detail
* Add the possibility to filter by Milestone and / or Assignee in the
  Merge Requests listing page

Merge branch 'master' into non-interactive-aws-install

Conflicts:
	doc/installation.md

Fix merge mess in installation.md

Didn't bother with files in db/, config/, or features/

* .page_title  class added. Used for better page headers
* improved help page
* added back links for help pages
* show app version & revision on help page

Backend changes:
* Gitab::Version && Gitlab::Revision constants