Added protocol fields for WebRTC signalling

Provides a simple wrapper around Javascript Session Establishment Protocol (JSEP)
JSON messages.

See https://tools.ietf.org/html/draft-ietf-rtcweb-jsep-03

Change-Id: I6b664369322e4682d4a8a2d62bcd4b84531a684f
Merge "Added protocol fields for WebRTC signalling"