REFACTOR: Move javascript tests inside discourse app

This is where they should be as far as ember is concerned. Note this is
a huge commit and we should be really careful everything continues to
work properly.

lib/generators/plugin/templates/acceptance-test.js.es6.erb

@@ -1,4 +1,4 @@
-import { acceptance } from "helpers/qunit-helpers";
+import { acceptance } from "discourse/tests/helpers/qunit-helpers";
 
 acceptance("<%= name %>", { loggedIn: true });