slopes.waymarkedtrails: Mark oneways on all piste types

[ppete2]

Right now on slopes.waymarkedtrails.org just alpine skiing pistes are marked with arrows. A very wise feature. So it would be fine, if all other types of pistes (nordic, skitour, sled) which are tagged as oneway would rendered with arrows as well.

Example of a oneway Nordic route: https://www.openstreetmap.org/way/691089586