Add support for custom sell cursors.

OpenRA.Mods.Common/Traits/Sellable.cs

@@ -27,6 +27,9 @@ namespace OpenRA.Mods.Common.Traits
 		[Desc("Skip playing (reversed) make animation.")]
 		public readonly bool SkipMakeAnimation = false;
 
+		[Desc("Cursor type to use when the sell order generator hovers over this actor.")]
+		public readonly string Cursor = "sell";
+
 		public override object Create(ActorInitializer init) { return new Sellable(init.Self, this); }
 	}