Introduce IMouseBounds and split/rework mouse rectangles.

The render bounds for an actor now include the area covered
by bibs, shadows, and any other widgets. In many cases this
area is much larger than we really want to consider for
tooltips and mouse selection.

An optional Margin is added to Selectable to support cases
like infantry, where we want the mouse area of the actor
to be larger than the drawn selection box.

OpenRA.Game/Orders/GenericSelectTarget.cs

@@ -10,6 +10,7 @@
 #endregion
 
 using System.Collections.Generic;
+using OpenRA.Graphics;
 using OpenRA.Traits;
 
 namespace OpenRA.Orders
@@ -62,7 +63,7 @@ namespace OpenRA.Orders
 			return world.Map.Contains(cell) ? Cursor : "generic-blocked";
 		}
 
-		public override bool InputOverridesSelection(World world, int2 xy, MouseInput mi)
+		public override bool InputOverridesSelection(WorldRenderer wr, World world, int2 xy, MouseInput mi)
 		{
 			// Custom order generators always override selection
 			return true;