Merge branch 'control-dropdown-permissions' into 'master'

Hide group control nav if no options present

Taken from https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/5155

See merge request !701

app/views/layouts/nav/_group.html.haml

+= render 'layouts/nav/group_settings'
 .scrolling-tabs-container{ class: nav_control_class }
-  = render 'layouts/nav/group_settings'
   .fade-left
     = icon('angle-left')
   .fade-right

app/views/layouts/nav/_group_settings.html.haml

 - if current_user
+  - can_admin_group = can?(current_user, :admin_group, @group)
   - can_edit = can?(current_user, :admin_group, @group)
   - member = @group.members.find_by(user_id: current_user.id)
   - can_leave = member && can?(current_user, :destroy_group_member, member)
 
+  - if can_admin_group || can_edit || can_leave
     .controls
       .dropdown.group-settings-dropdown
         %a.dropdown-new.btn.btn-default#group-settings-button{href: '#', 'data-toggle' => 'dropdown'}