REFACTOR: Import QUnit and related helpers rather than globals

We used many global functions to handle tests when they should be
imported like other libraries in our application. This also gets us
closer to the way Ember CLI prefers our tests to be laid out.

app/assets/javascripts/discourse-loader.js

@@ -153,6 +153,19 @@ var define, requirejs;
       pretender: {
         default: window.Pretender,
       },
+      "ember-qunit": {
+        moduleFor: window.moduleFor,
+        moduleForComponent: window.moduleForComponent,
+      },
+      qunit:
+        typeof window.QUnit !== "undefined"
+          ? {
+              default: window.QUnit,
+              test: window.QUnit.test,
+              skip: window.QUnit.skip,
+              module: window.QUnit.module,
+            }
+          : undefined,
     };
   }