Fallback to English when the Dutch translation isn't available.
Added the Rails engine Kuva.
The carousel partial requires the instance variable @article to be available in each view. Since Kuva doesn't have that in its controllers, we need to set it in the ApplicationController, which will also be loaded through Kuva. Therefore we can remove it from all other controllers.
The URL's used in the main Rails application require the prefix main_app, otherwise it will look for the URL's in the Kuva Rails engine.
Added the Kuva URL to the descriptive navigation.
Actually mount the Kuva Rails engine and load its assets.