HG-16: Mercury API Extension

DO NOT MERGE, THIS PR IS PART OF PROJECT MERCURY! 
We wanted to experiment with much lighter approach to JSONifying artilcle
have a look at https://github.com/Wikia/app/pull/3838

This needs some cleanup but works well for us
We can talk about it this week if you have time.

And yes there is an existing API to get Json for an article but is too verbose for what we're trying to achieve here.