Support and examples for Ember.Object and Ember.Controller imports

We should stop using global variables and instead import these as
needed.

app/assets/javascripts/discourse-loader.js

@@ -6,6 +6,8 @@ var define, requirejs;
   if (typeof Ember !== "undefined") {
     EMBER_MODULES = {
       "@ember/component": { default: Ember.Component },
+      "@ember/controller": { default: Ember.Controller },
+      "@ember/object": { default: Ember.Object },
       "@ember/routing/route": { default: Ember.Route }
     };
   }