[Ember] Add definition for Ember.RSVP.Promise constructor

are you sure about `label`. Its not there in our es6-promise lib : https://github.com/borisyankov/DefinitelyTyped/blob/master/es6-promises/es6-promises.d.ts#L23 which is a part of the RSVP collection of libs + I don't see it here : http://emberjs.com/api/classes/Ember.RSVP.Promise.html