Move Cloak, HiddenUnderFog, FrozenUnderFog into Mods.RA; Simplify a pile of related stuff.

OpenRA.Game/Traits/Unit.cs

@@ -48,11 +48,7 @@ namespace OpenRA.Traits
 		}
 		
 		public IEnumerable<int2> RadarSignatureCells(Actor self)
-		{
-			foreach (var mod in self.traits.WithInterface<IRadarVisibilityModifier>())
-				if (!mod.VisibleOnRadar(self))
-					yield break;
-			
+		{	
 			yield return self.Location;
 		}