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/Widgets/WorldInteractionControllerWidget.cs

@@ -164,7 +164,7 @@ namespace OpenRA.Widgets
 		IEnumerable<Actor> SelectActorsInBox(World world, PPos a, PPos b, Func<Actor, bool> cond)
 		{
 			return world.FindUnits(a, b)
-				.Where( x => x.HasTrait<Selectable>() && world.LocalShroud.IsVisible(x) && cond(x) )
+				.Where( x => x.HasTrait<Selectable>() && world.RenderedShroud.IsVisible(x) && cond(x) )
 				.GroupBy(x => x.GetSelectionPriority())
 				.OrderByDescending(g => g.Key)
 				.Select( g => g.AsEnumerable() )