Added last modified sort button

notebook/static/tree/less/tree.less

@@ -188,6 +188,11 @@ ul.breadcrumb {
     }
 }
 
+#last_modified {
+    display: inline-block;
+    padding-left: @dashboard_lr_pad;
+}
+
 #tree-selector {
     padding-right: 0px;
 }

notebook/templates/tree.html

@@ -101,6 +101,11 @@ data-terminals-available="{{terminals_available}}"
                 {% endfor %}
                 </ul>
               </div>
+              <div id="last_modified" class="pull-right">
+                  <span class="btn btn-xs btn-default" id="button-last-modified">
+                      Last Modified
+                  </span>
+              </div>
             </div>
           </div>
         </div>