RTCMultiConnection-v1.2, DataChannel, users ejection and presence detection

Many new features added in DataChannel.js and RTCMultiConnection.js

DataChannel.js now supports auto session establishment:

https://webrtc-experiment.appspot.com/DataChannel/auto-session-establishment/

RTCMultiConnection.js now supports:
1. Manual session establishment
2. Extra data transmission
3. Users Ejection and their presence detection
https://webrtc-experiment.appspot.com/#RTCMultiConnection

https://webrtc-experiment.appspot.com/RTCMultiConnection/users-ejection/