WebClient: add a ping URL

Signed-off-by: Nicola Murino <nicola.murino@gmail.com>

templates/webclient/editfile.html

@@ -105,8 +105,9 @@ explicit grant from the SFTPGo Team (support@sftpgo.com).
     var cmView;
 
     function keepAlive() {
-        axios.get('{{.ProfileURL}}',{
-            timeout: 15000
+        axios.get('{{.PingURL}}',{
+            timeout: 15000,
+            responseType: 'text'
        	}).catch(function (error){});
     }