Destroy peer connections on socket close
Handle removestream event

Remove stream is called after the remote peer has called removeStream
and renegotiated.
See: https://code.google.com/p/webrtc/issues/detail?id=1510
Handle close of remote peer connection

Peer connection does not contain give an onclose event. Use the ICE
connection state to determine close.
See:
https://code.google.com/p/webrtc/issues/detail?id=1676
http://dev.w3.org/2011/webrtc/editor/webrtc.html#rtciceconnectionstate-enum
Tidy up destroyPeerConnection