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.
Ah, sorry. I misread this. I see the datachannel is called `text`. `a` doesn't get the `peerOpenedChannelQueue` event so has to call the `connectDataChannel` after creating the data channel.

:+1: