* Add session_t typedef + remove unused functions
u16 peer_id is used everywhere, to be more consistent and permit some evolutions on this type in the future (i'm working on a PoC), uniformize u16 peer_id to SessionId peer_id
Implement network communication for channels
* Implement ModChannel manager server side to route incoming messages from clients to other clients
* Add signal handler switch on client & ModChannelMgr on client to handle channels
* Add Lua API bindings + client packet sending + unittests
* Implement server message sending
* Add callback from received message handler to Lua API using registration method