Merge branch 'mobile_menu_help' into 'master'

Fix mobile menu after adding help link

After https://github.com/gitlabhq/gitlabhq/pull/6897 the mobile menu ran off the left side of the screen. I don't see much we can do to squeeze all the items into mobile's width. I think hiding one of the items is acceptable and which is a matter of opinion.  I suggest hiding the user's avatar on mobile but the search icon or help icon would both be options as well. Let me know if you want a different icon hidden on mobile.

[Before Screenshot](https://www.dropbox.com/s/hnfmaln3ilcy0p7/Screen%20Shot%202014-05-02%20at%205.17.28%20PM.png)
[After Screenshot](https://www.dropbox.com/s/3ifxa8gfa12h37h/Screen%20Shot%202014-05-05%20at%204.52.25%20AM.png)

app/views/layouts/_head_panel.html.haml

@@ -43,6 +43,6 @@
           %li
             = link_to destroy_user_session_path, class: "logout", method: :delete, title: "Logout", class: 'has_bottom_tooltip', 'data-original-title' => 'Logout'  do
               %i.icon-signout
-          %li
+          %li.hidden-xs
             = link_to current_user, class: "profile-pic", id: 'profile-pic' do
               = image_tag avatar_icon(current_user.email, 26), alt: 'User activity'