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/Graphics/Viewport.cs

@@ -202,7 +202,7 @@ namespace OpenRA.Graphics
 				cachedScroll = scrollPosition;
 			}
 
-			var b = world.LocalShroud.Bounds;
+			var b = world.RenderedShroud.Bounds;
 			return (b.HasValue) ? Rectangle.Intersect(cachedRect, b.Value) : cachedRect;
 		}
 	}