Gridfinity Windsor & Newton ink bottle holder

Windsor & Newton drawing ink bottle holders for #gridfinity.

Because I don't use the screwholes, they're only really deep enough to allow magnet installation. That allows the ink bottle to sit a little lower than it would otherwise.

This was built using CadQuery - source here: https://github.com/sffubs/gridfinity/blob/master/windsor_and_newton_ink_holder.py