Ajax wrapper

- added $.ajax, $.getJSON wrapper inspired by [discourse ajax](https://github.com/discourse/discourse/blob/master/app/assets/javascripts/discourse/mixins/ajax.js).
- added Ember shorthand `Em`
- added new Globe trac link

Using the `GLOBE.ajax` or `GLOBE.getJSON`  returns a RSVP.Promise that calls resolve or reject with `Ember.run`. This way it won't break on async operations if Ember testing is active.