Hg 69 consolidate api

Consolidate some API entry points
so we don't have to make so many requests for one article
@kenkouot @benmai @aquilax 
I guess the idea here is this to be used as entry point and from `getArticle` but currently it won't work as Nirvana entry point. I get 
```
Argument 1 passed to MercuryApi::topContributorsPerArticle() must be an instance of Title, array given
```
Also the result is an array and the response is not set.

My guess can also be wrong :)