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- RenderNameTag has been replaced by WithNameTagDecoration, which is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.Mods.Common/TraitsInterfaces.cs

@@ -15,6 +15,7 @@ using OpenRA.Activities;
 using OpenRA.Graphics;
 using OpenRA.Mods.Common.Activities;
 using OpenRA.Mods.Common.Graphics;
+using OpenRA.Mods.Common.Traits.Render;
 using OpenRA.Primitives;
 using OpenRA.Traits;
 
@@ -642,4 +643,40 @@ namespace OpenRA.Mods.Common.Traits
 	{
 		string Class { get; }
 	}
+
+	public interface IDecoration
+	{
+		DecorationPosition Position { get; }
+		bool RequiresSelection { get; }
+
+		bool Enabled { get; }
+
+		IEnumerable<IRenderable> RenderDecoration(Actor self, WorldRenderer wr, int2 pos);
+	}
+
+	public enum DecorationPosition
+	{
+		Center,
+		TopLeft,
+		TopRight,
+		BottomLeft,
+		BottomRight,
+		Top
+	}
+
+	public static class DecorationExtensions
+	{
+		public static int2 CreateMargin(this DecorationPosition pos, int2 margin)
+		{
+			switch (pos)
+			{
+				case DecorationPosition.TopLeft: return margin;
+				case DecorationPosition.TopRight: return new int2(-margin.X, margin.Y);
+				case DecorationPosition.BottomLeft: return new int2(margin.X, -margin.Y);
+				case DecorationPosition.BottomRight: return -margin;
+				case DecorationPosition.Top: return new int2(0, margin.Y);
+				default: return int2.Zero;
+			}
+		}
+	}
 }