Introducing per-player shrouds.

- Each player has their own shroud and their visibility does not extend outside of the shroud. 
- Units and buildings can no longer target other units outside of their visibility. Buildings can still be targetted if they have been explored.
- GPS will provide visibility in the fog-of-war.
- Spies that infiltrate radar domes will gain their victim's exploration and reset it on all clients (if the victim does not have GPS)

OpenRA.Game/Network/UnitOrders.cs

@@ -198,8 +198,7 @@ namespace OpenRA.Network
 		{
 			var oldStance = p.Stances[target];
 			p.Stances[target] = s;
-			if (target == w.LocalPlayer)
-				w.WorldActor.Trait<Shroud>().UpdatePlayerStance(w, p, oldStance, s);
+			target.Shroud.UpdatePlayerStance(w, p, oldStance, s);
 
 			foreach (var nsc in w.ActorsWithTrait<INotifyStanceChanged>())
 				nsc.Trait.StanceChanged(nsc.Actor, p, target, oldStance, s);