Make use of new P2pNet channel data

[jimkberry]

Part of this might be an apian issue, but since p2p "hello" data is now district per-channel, for Beam there are 2 different levels of P2p hello data, and the addition JoinGroupRequest data. So there's:

• ApianNetwork (p2p main channel) P2pNet hello
• ApianGame (p2p channel for ApianGroup) P2pNet Hello
• ApianJoinGroupRequest data:

Currently we:

• Pass a BeamGameNet-encoded BeamPeer representing the local peer to GameNet.JoinNetwork()
  Which shows up in BeamApplication.OnPeerJoinedNetwork and has do be JSON-decoded there.
• Pass null to GameNet.AddChannel() from ApianGameNet.JoinGroup() - so other peers' P2pNet instances get null as our "hello" data for that channel.
• Pass a BeamPlayer.ApianSerialized() representing the local "player" (PeerId + Name) in our game GroupJoinRequest.

Note that BeamNetworkPeer and BeamPlayer are both application-defined class, and are pretty much identical.

Yuk.

[jimkberry]

We no longer set the P2pNet channel localData to null - it was ugly having null as the peer-specific channel data for remote peers. On the other hand, it's now just set to a constant placeholder string and not used for anything.

We could pass the local peer's version of the channelInfo - and I guess it could be used for making sure everyone is on the same page? Seems like a waste, tho.