This allows for more use cases to be handled like having several session
between 2 peers, and it simplifies the code a bit and makes the protocol
sensibly cleaner
Webrtcsink has been refactored a bit to take the new concept into
account
This way we can use the same WebSocket where several peerTypes being
communicated and some those type can be unregistered, re registered
without ever closing the Socket connection.
This also introduces sensible symmetry between different message types.
In some applications people might need to be able to pass more metadata
than the only "display-name" this commit allow that by adding a field in
all signalling structure where it is free form json and removing the
"display-name" as the free form `meta` field allows application to pass
this kind of information without any problem.
On the "webrtcsink" side this commit adds a `meta` property as a
gst::Structure which will be passed as a json string to the signalling
server so we enforce data to be structured.
