Disable adding members from admin area when appropriate

app/views/admin/groups/show.html.haml

@@ -51,6 +51,7 @@
         = paginate @projects, param_name: 'projects_page', theme: 'gitlab'
 
   .col-md-6
+    - if can?(current_user, :admin_group_member, @group)
       .panel.panel-default
         .panel-heading
           Add user(s) to the group:
@@ -86,6 +87,7 @@
                 (invited)
             %span.pull-right.light
               = member.human_access
+              - if can?(current_user, :destroy_group_member, member)
                 = link_to group_group_member_path(@group, member), data: { confirm: remove_user_from_group_message(@group, member) }, method: :delete, remote: true, class: "btn-xs btn btn-remove", title: 'Remove user from group' do
                   %i.fa.fa-minus.fa-inverse
       .panel-footer