Gds upgrade remove rabl

Content api like you've never seen it before!!!! :horse: :cat2: 

Removes a LOAD of stuff you don't use or need which makes it a hell of a lot clearer to see what's going on.

No longer uses RABL. It's now done with a bunch of presenters, this *should* make it clearer for you to see what's going on and give a performance boost.

Increased test coverage.

DO NOT MERGE until Gavin is no longer on TV being interviewed :scream_cat: