WebRTC.MediaHandler#createOfferOrAnswer: var pc = self.peerConnection;
WebRTC.MediaHandler#createOfferOrAnswer: promisify setting local sdp
define Utils.defer()
WebRTC.MediaHandler#createOfferOrAnswer: promisify onSetLocalDescriptionSuccess
WebRTC.MediaHandler#createOfferOrAnswer: define handlers in .then()
WebRTC.MediaHandler#createOfferOrAnswer: return a promise
WebRTC.MediaHandler: use a deferred for onIceCompleted

WebRTC.MediaHandler: emit 'iceComplete' outside of createOfferOrAnswer
WebRTC.MediaStreamManager#acquire: flatten code by using a deferred
(Non)InviteClientTransaction#receiveResponse: return a promise