added Ember.ajax

I don't really get how this all works. Please tell me what I need to change.

1. Where should I assign Ember.ajax = ic.ajax?
2. How do I document this as Ember.ajax, and make sure it shows up in the docs for the website, etc?
3. do we care that the global `ic` is floating around?
4. what does the package.json need to look like in packages/ic-ajax/package.json?
5. when will the world agree on javascript module formats? :love_letter: 
6. should this be behind a feature flag?