Made EventWindow into a singleton.

app/js/ui/EventWindow.js

-import '/app/js/EventCaller.js'
+import {EventCaller} from '/app/js/EventCaller.js'
 
 /**
  *  Wraps the browser's window object around the EventCaller allowing the user to connect to system events
  *
  *  Users should not directly set the window event handler functions if using this class.
  */
-export class EventWindow extends EventCaller{
+class EventWindow extends EventCaller{
   constructor(){
     super();
+    if (!EventWindow.instance)
+      EventWindow.instance = this;
+    return EventWindow.instance;
   }
 
   listen(eventName, callback, owner=null, once=false){
     return this;
   }
 }
+
+
+const instance = new EventWindow();
+Object.freeze(instance);
+export default instance;
+