add basic user revert functionality

app/views/post_versions/index.html.erb

@@ -7,6 +7,10 @@
     <% else %>
       <%= render "listing", :post_versions => @post_versions %>
 
+      <% if params[:lr] && CurrentUser.is_janitor? %>
+        <p><%= link_to "Revert this user's changes", new_user_revert_path(:user_id => params[:lr]) %></p>
+      <% end %>
+
       <%= numbered_paginator(@post_versions) %>
     <% end %>
   </div>