Support notification and display of player joined/left/missing/returned events

[jimkberry]

It's already kinda/sorta there - but needs to be made more consistent - but these 4 events should be available to a BeamFrontend.

This can happen either via:

• GamNet -> Apian -> appCore -> Frontend
• GameNet -> ApianApplication -> Frontend

Missing/returned is currently done per-apian group using the former There is some infrastructure for doing network-level (as opposed to group-level) peer join and leave via the latter

2 results are needed: a) Both the Unity and Cli implmentation frontends need to report them (actually, should report net-level stuff too) b) Code for the whole thing should be made consistent

Either can happen first.

[jimkberry]

I think the correct thing to do here is:

• OnPeerMissing() and OnPeerReturned() should be added to the IGameNetClient interface and called by the base GameNet implementation if a peer is reported missing or returned by the main "network" channel. Note that this is all about a PEER's presence in the P2pNet idea of a "network".
• ApianGameNet's override of the GameNet methods which do the above dispatch will also dispatch those messages to any Apian instance using that particular "channel" before calling the base implementation.

So: the iGameNetClient gets notified about events related to the main net channel, and Apian gets the others.

[jimkberry]

Done