Rework decoration renderable traits:

- Removed implicit pip definitions and IPips interface.
  New decoration traits have been added to render them.
  Pip types are no longer hardcoded in OpenRA.Game.

- Decoration rendering is now managed by SelectionDecorations(Base),
  which allows us to remove assumptions about the selection box
  geometry from the decoration traits.

- RenderNameTag has been replaced by WithNameTagDecoration, which is
  an otherwise normal decoration trait.

- Unify the configuration and reduce duplication between traits.

- Removed hardcoded references to specific selection box renderables.

- Remove legacy cruft.

OpenRA.Game/Primitives/Rectangle.cs

@@ -66,6 +66,11 @@ namespace OpenRA.Primitives
 		public int2 Location { get { return new int2(X, Y); } }
 		public Size Size { get { return new Size(Width, Height); } }
 
+		public int2 TopLeft { get { return Location; } }
+		public int2 TopRight { get { return new int2(X + Width, Y); } }
+		public int2 BottomLeft { get { return new int2(X, Y + Height); } }
+		public int2 BottomRight { get { return new int2(X + Width, Y + Height); } }
+
 		public bool Contains(int x, int y)
 		{
 			return x >= Left && x < Right && y >= Top && y < Bottom;