Smart new channel join

[lucabaldesi]

Currently, if one plays the same channel on different tabs PS-ng creates two new streaming instances.
This is suboptimal as there is no need of further signalization and data transfer beyond one acquisition.
Streaming the second time a channel already streamed should result in just the doubling of the last-link toward Janus and WebRTC.

Ideally, this should be implemented at the de-chunkiser level.