RTCMultiConnection updated. Relevant demos fixed

All-in-One test:
https://webrtc-experiment.appspot.com/RTCMultiConnection/

Video Conferencing:

https://webrtc-experiment.appspot.com/RTCMultiConnection/video-conferencing/

Audio Conferencing:

https://webrtc-experiment.appspot.com/RTCMultiConnection/audio-conferencing/

Now, you can set `autoCloseEntireSession` before calling `leave` method;
which will enforce closing of the entire session:

connection.autoCloseEntireSession = true;
connection.leave(); // closing entire session