Dig and dump grade options to match train elevation option

Not sure how to describe that better...
It would be cool to dig/dump/level a minimum grade incline for future tracks.

You can do this today, mostly, it's just a pain to do it. Basically every tile you need to alternate between flat and elevated. Then when you run the 12% incline on the train down it, it runs very close to the ground, touching on the edges.