[GOMPS-470] cleaning up todos and fixmes

[dwoodruffsf]

Main changes:

• cleaned up miscellaneous todos and fixmes
• Added plumbing so that the server can explicitly set a DisconnectReason on a client (the motivation for this was the "GUID Already Playing" error condition, where the server wants to boot the old connection, and give a reason).
• Found ConnectStatus and DisconnectReason to be highly duplicative, so I combined them into ConnectStatus
• Updated Client logic to detect Host disconnect scenario (e.g. host losing network).
• ServerGameNetPortal now properly cleans up per-connection state on client disconnect.
• ServerGameNetPortal now handles two more error cases: (1) server full, and (2) guid already playing (in the latter case, kicks the old connection).
• ServerGameNetPortal now actually disconnects you if you experience a game-level connection failure.
• GameNetPortal: Some Named Messages were being missed because they were arriving before the ClientConnected callback. I moved this event registration to Start, and made it unconditional on the role.
• Brought back workaround in ServerCharSelectState to prevent GOMPS-506 and GOMPS-508 from blocking entry into game.

I have left two FIXME:MLAPI and 1 TODO:MLAPI tag in the code, referencing active MLAPI bugs in the first case, and a feature we are expecting in the future in the second.

[fernando-cortez]

My comments have been addressed.