Port WebRtc.PeerConnection to freedom-0.6's core.rtcpeerconnection.

This is a very rough draft with regard to code style, but it does
include a version of simple-freedom-chat that uses the new
WebRtc.PeerConnection.  This is working in Chrome, but not yet in
Firefox.
Suggestion: Glancing at this, I assumed `A` had some relationship with peer `a`. Perhaps use `X` or `TEST` (or any other string from any other namespace).