UI changes:

* .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

app/views/merge_requests/index.html.haml

@@ -1,4 +1,4 @@
-%h3
+%h3.page_title
   Merge Requests
   - if can? current_user, :write_issue, @project
     = link_to new_project_merge_request_path(@project), :class => "right btn small", :title => "New Merge Request" do

app/views/merge_requests/show/_mr_title.html.haml

@@ -1,4 +1,4 @@
-%h3
+%h3.page_title
   = "Merge Request ##{@merge_request.id}:"
    
   %span.pretty_label.branch= @merge_request.source_branch