In an app, we encourages users to use injection over container.lookup,
and we encourage `application.register` over `registry.register`. But in
our integration tests, there is no good alternative to direct
`this.container.lookup` and `this.registry.register`.

So I added `register` and `inject` capability directly to the
integration test context. `register` is fairly trivial:

    test('registering something', function(assert) {
      this.register('component:x-foo', Ember.Component.extend({
        classNames: ['i-am-x-foo']
      }));
      this.render(hbs`{{x-foo}}`);
      assert.equal(this.$('.i-am-x-foo').length, 1, 'found x-foo');
    });

`inject` lets you inject anything into the test context:

    test('injecting a service', function(assert) {
      this.inject.service('notifications');
      this.render(hbs`{{my-notification-viewer}}`);

      // The notifications service has been injected into our test context,
      // so we can access it here and tell it to do something.
      this.get('notifications').receivedNotification("Hello world");

      assert.equal(this.$('.notification').text(), 'Hello world');
    })

You can also give the injected thing an alternate name using `as`:

    test('injecting a service with aliased name', function(assert) {
      this.inject.service('notifications', { as: 'messages' });
      this.render(hbs`{{my-notification-viewer}}`);

      // The notifications service has been injected into our test context
      // as this.get('messages').
      this.get('messages').receivedNotification("Hello world");

      assert.equal(this.$('.notification').text(), 'Hello world');
    })