Rewrite production tabs (again): Avoid doing a pile of work every tick; support multiple queue types grouped under one category; Tab numbering is sticky.

OpenRA.Mods.RA/Player/ProductionQueue.cs

@@ -19,6 +19,8 @@ namespace OpenRA.Mods.RA
 	public class ProductionQueueInfo : ITraitInfo
 	{
 		public readonly string Type = null;
+		public readonly string Group = null;
+
 		public float BuildSpeed = 0.4f;
 		public readonly int LowPowerSlowdown = 3;