Serve basic pages from content-store

Get an item from the content store and display it on a page. Views are very basic at this point, and controller just passes the content hash directly to the page.

It should only be `government-frontend` when the new app is actually rendering the content on GOV.UK. For now, we're pushing case studies into content store with the existing whitehall frontend app as the rendering app. Once we are happy that the frontend app is fully rendering the content, we will switch the rendering app to `government-frontend`.