GraviTrax compatible track bases

Once you have enough [bridge piers](https://www.thingiverse.com/thing:2738439) and [track rails](https://www.thingiverse.com/thing:2738473) you eventually run out of the hexagonal track base plates with the curves engraved.
As the [GraviTrax original starter set](https://www.ravensburger.de/produkte/gravitrax/gravitrax-starter-set/gravitrax-starterset-27590/index.html) is still sold out, my son made me design something compatible for his marble run.

The Curved item is very similar to the ori