Objectize the AppRTC javascript and add unit tests

This is a big refactoring to make the javascript more object oriented and MVC.
I haven't added unit tests for all classes yet, but want to get some feedback before all reviewers are gone for vacation.
New classes:
AppController: the controller that connects the UI and the model "Call"
Call: manages everything needed to make a call
SignalingChannel: wrapper of the WebSocket connection
PeerConnectionClient: wrapper of RTCPeerConnection
InfoBox: wrapper of the info div

CC: @samdutton @tkchin @juberti