update static images

uws_client/templates/skeleton.html

@@ -31,7 +31,7 @@
     <div id="loading_div"
          style="position: fixed; top:5px; left:5px; width:2%; z-index: 10; opacity: 0.8;">
         <div id="loading" class="col-md-12" style="display:none;">
-            <img src="/static/images/loading.gif" alt="loading" height="50" width="50"/>
+            <img src="/static/images/loading.png" alt="loading" height="50" width="50"/>
         </div>
     </div>
     <div id="messages_div"