Remove harvester dependency on RenderUnit.

OpenRA.Game/Traits/TraitsInterfaces.cs

@@ -74,6 +74,8 @@ namespace OpenRA.Traits
 	public interface INotifyOwnerChanged { void OnOwnerChanged(Actor self, Player oldOwner, Player newOwner); }
 	public interface INotifyCapture { void OnCapture(Actor self, Actor captor, Player oldOwner, Player newOwner); }
 	public interface INotifyOtherCaptured { void OnActorCaptured(Actor self, Actor captured, Actor captor, Player oldOwner, Player newOwner); }
+	public interface INotifyHarvest { void Harvested(Actor self, ResourceType resource); }
+
 	public interface IAcceptInfiltrator { void OnInfiltrate(Actor self, Actor infiltrator); }
 	public interface IStoreOre { int Capacity { get; } }
 	public interface IToolTip