Add x_content to plain page

To avoid missing a class 'x_content' when prototyping a page layout

production/plain_page.html

@@ -357,6 +357,9 @@
                     </ul>
                     <div class="clearfix"></div>
                   </div>
+                  <div class="x_content">
+                      Add content to the page ...
+                  </div>
                 </div>
               </div>
             </div>
@@ -387,4 +390,4 @@
     <!-- Custom Theme Scripts -->
     <script src="js/custom.js"></script>
   </body>
-</html>
+</html>