Make ITick require explicit implementation

OpenRA.Game/Traits/TraitsInterfaces.cs

@@ -92,6 +92,7 @@ namespace OpenRA.Traits
 		}
 	}
 
+	[RequireExplicitImplementation]
 	public interface ITick { void Tick(Actor self); }
 	public interface ITickRender { void TickRender(WorldRenderer wr, Actor self); }
 	public interface IRender { IEnumerable<IRenderable> Render(Actor self, WorldRenderer wr); }