Hg 69 use one api

There is still some cleanup to do
but maybe you can already spot something that I did that needs to be fixed
@kenkouot @benmai 
I think it's a good idea to have an Ember abstraction for Wiki data so we minimize interacting directly with the Wikia object, but I think it should not be in ArticleModel. In my PR #110 I access Wikia.wiki for navigation data, which is independent of ArticleModel. Perhaps it should have its own model?