(js) Fix download of exported folders under iOS

Whenever possible, we no longer rely on the FileSaver.js library to
download zip archives. Instead, we do a simple GET on the resource by
changing the window location.

UI/WebServerResources/js/Scheduler/Calendar.service.js

@@ -554,7 +554,7 @@
       filename: this.name + '.ics'
     };
 
-    return Calendar.$$resource.download(this.id + '.ics', 'export', null, options);
+    return Calendar.$$resource.open(this.id + '.ics', 'export', null, options);
   };
 
   /**