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.Mods.Common/Traits/Modifiers/FrozenUnderFog.cs

@@ -128,6 +128,7 @@ namespace OpenRA.Mods.Common.Traits
 		{
 			IRenderable[] renderables = null;
 			Rectangle[] bounds = null;
+			Rectangle mouseBounds = Rectangle.Empty;
 			for (var playerIndex = 0; playerIndex < frozenStates.Count; playerIndex++)
 			{
 				var frozen = frozenStates[playerIndex].FrozenActor;
@@ -139,6 +140,7 @@ namespace OpenRA.Mods.Common.Traits
 					isRendering = true;
 					renderables = self.Render(wr).ToArray();
 					bounds = self.ScreenBounds(wr).ToArray();
+					mouseBounds = self.MouseBounds(wr);
 
 					isRendering = false;
 				}
@@ -146,6 +148,7 @@ namespace OpenRA.Mods.Common.Traits
 				frozen.NeedRenderables = false;
 				frozen.Renderables = renderables;
 				frozen.ScreenBounds = bounds;
+				frozen.MouseBounds = mouseBounds;
 				self.World.ScreenMap.AddOrUpdate(self.World.Players[playerIndex], frozen);
 			}
 		}