WebRTC Part of Screen Sharing updated

Share part of screen using RTCDataChannel:

https://googledrive.com/host/0B6GWd_dUUTT8RzVSRVU2MlIxcm8/part-of-screen-sharing/RTCDataChannel/

Sharing part of screen using Firebase:

https://googledrive.com/host/0B6GWd_dUUTT8RzVSRVU2MlIxcm8/part-of-screen-sharing/