Wrap uploadAllFiles' return value in an Ember.RSVP.Promise.

Fixes race condition getting the result of the `jQuery.then`; you might've got undefined because of Ember's run loop. Also callers don't have to think about jQuery any more.
Merge pull request #64 from CrowdStrike/promisify-all-the-things

Wrap uploadAllFiles' return value in an Ember.RSVP.Promise.