CivClash: Nation PVP

This is still prealpha. I fixed some bugs and expanded on the implementation around diplomacy and adding/joining or leaving a nation.

Fixed:
rendering bugs in claim maps and overlay;
client crash when admin removes claims;
unclaiming land as player;
not being able to leave as last player in nation;
not being able to found new nation after disbanding a nation;

Implemented:
offline player status tracking;
join command;
Diplomacy status rendering on nation map;
Network packets update client on nation changes;