HG-16: Mercury API Extension

DO NOT MERGE, THIS PR IS PART OF PROJECT MERCURY! 
This is hacky now and I intended to refactor this after getting some feedback if direction is good

if $wgArticleAsJson is set to true article is being saved as json to memcache thats why it works

again speed of development of an experiment, it proves that it works for us, now we have to think how to make it clean.

If you have time this week we might discuss some of this stuff.

Thanks