Add disable gravatar option

templates/admin/config.tmpl

@@ -181,6 +181,8 @@
                 <dl class="dl-horizontal admin-dl-horizontal">
                     <dt>Picture Service</dt>
                     <dd>{{.PictureService}}</dd>
+                    <dt>Disable Gravatar</dt>
+                    <dd><i class="fa fa{{if .DisableGravatar}}-check{{end}}-square-o"></i></dd>
                 </dl>
             </div>
         </div>