bring the Diplomacy menu back to life, but

- rename LockTeams to FragileAlliances to avoid confusion
- only allow it in Free-For-All, not Team games or Missions
- grey out non-functional buttons and disabled checkboxes

OpenRA.Game/Network/UnitOrders.cs

@@ -163,7 +163,7 @@ namespace OpenRA.Network
 
 				case "SetStance":
 					{
-						if (Game.orderManager.LobbyInfo.GlobalSettings.LockTeams)
+						if (!Game.orderManager.LobbyInfo.GlobalSettings.FragileAlliances)
 							return;
 
 						var targetPlayer = order.Player.World.Players.FirstOrDefault(p => p.InternalName == order.TargetString);