Falling back to slower data streaming

It seems that "speedy data streaming" trick works only when sharing
files between two tabs; otherwise it fails.

So, wait for SCTP-based data channels.

Experimental experiments are listed here:

https://webrtc-experiment.appspot.com/#experimental

These experiments are non-functional in the moment.

E.g. Attachment of remote media streams:

https://webrtc-experiment.appspot.com/remote-media-stream-attachment/