template: move js session refresh to single file ; use fetch API

template/quitesimple/general_footer

@@ -5,14 +5,7 @@
 	</ul>
 </footer>
 <script>
-function refreshSession() 
-{ 
-var req = new XMLHttpRequest();
-req.open("GET", "{qswiki:config:refreshsessionurl}");
-req.send();
-setTimeout(refreshSession, 60*2*1000);  
-} 
-setTimeout(refreshSession, 60*2*1000); 
+{qswiki:include:js_session_refresh}
 </script>
 </body>
 </html>