More shroud refactoring.

This introduces a hash on Shroud which ShroudRenderer
can observe, removing the need to explicitly twiddle
a dirty flag between objects.

Shroud disabling is now done via RenderPlayer, so
enabling the cheat or winning/losing will now give
vis equivalent to an observer.

OpenRA.Mods.RA/Widgets/Logic/IngameChatLogic.cs

@@ -30,7 +30,7 @@ namespace OpenRA.Mods.RA.Widgets.Logic
 		private bool teamChat = false;
 		internal bool TeamChat
 		{
-			get { return World.Observer ? false : teamChat; }
+			get { return World.LocalPlayer == null ? false : teamChat; }
 			set { teamChat = value; }
 		}