Webpack refactor

- added JSX support (webpack + robofile
- added public.js bundle
- refactored webpack config for clarity
- added settings.jsx form example
- fixed acceptance test failing on login

assets/js/src/admin.js

@@ -1,12 +1,13 @@
 define('admin', [
     'mailpoet',
-    'jquery',
-    'handlebars',
-  ], function(MailPoet, jQuery, Handlebars) {
-  jQuery(function($) {
-    // dom ready
-    $(function() {
+    'jquery'
+  ],
+  function(MailPoet, jQuery) {
+    jQuery(function($) {
+      // dom ready
+      $(function() {
 
+      });
     });
-  });
-});
+  }
+);