DataChannel bandwidth test and WebRTCCall to help doing loopback calls.

Added WebRTCCall to help establishing a calling between two local peer connections.

Implemented a DataChannel bandwidth test that sends a block of packets of 1024 bytes
everytime the bufferedAmount is 0 and prints the bitrate sent over one second.
There is going to be ramp-up, so I think we want to sample this every second and print out the value each second (for now).