Allow picking TURN/UDP or TURN/TCP in url params

Also, clean up some legacy TURN-related URL parameters that were
obsolete.  You can now specify a HTTP URL for TURN via ts=, but the
previous ts, tp, ss parameters are now defunct.
Resolve PR comments
Expanded comments regarding it/tt.
Added unit tests
Merge pull request #312 from GoogleChrome/tt

Allow picking TURN/UDP or TURN/TCP in url params