Standardised module loading system & fixed build system

Fixed broken build system in broken webpack version.
Also updates module system to standardise on ES6 import/exports,
Especially since babel has changed it's 'default' logic for the old
module system.

resources/assets/js/components/entity-selector-popup.js

@@ -44,4 +44,4 @@ class EntitySelectorPopup {
     }
 }
 
-module.exports = EntitySelectorPopup;
+export default EntitySelectorPopup;