Added OwnerLostAction

Allows customisation of what will happen to an actor when its owner
loses.

OpenRA.Mods.Common/Traits/Player/ConquestVictoryConditions.cs

@@ -70,8 +70,8 @@ namespace OpenRA.Mods.Common.Traits
 
 		public void OnPlayerLost(Player player)
 		{
-			foreach (var a in player.World.Actors.Where(a => a.Owner == player))
-				a.Kill(a);
+			foreach (var a in player.World.ActorsWithTrait<INotifyOwnerLost>().Where(a => a.Actor.Owner == player))
+				a.Trait.OnOwnerLost(a.Actor);
 
 			if (info.SuppressNotifications)
 				return;