Train filter - option of none

In the Train line manager filter options, we have load anything or load/unload an item(s) on a filter. I think we also need an option to load/unload none. This would allow us to more easily build complex rail networks.

This would also allow us to load/unload mixed cargo like raw mine output, with dirt, stone and ore mixed.
It would add much more value to the new huge ore sorting plants, allowing trains from multiple mines dumping stuff into one big factory.

I would say while we are improving the logic for stations, it should be added that a train only unload/load specified goods. Not whatever fits in the car for that station position. This would make multi-product stations more viable when you have a train that isn't going to the unload destination for that product.

Thank you, Devs!