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.
Done.. the test now runs for 5 seconds and also prints a total in the end. We can revise later once we have tests that run via a turn server or via server reflex candidates.