Ikea Lack Printer enclosure foot easier to print

Original foot was solid and hard to print. Flipped the model, hollowed out the interior and angled the glass supports. Recommend printing with supports and raft due to limited surface area on the bottom, but the glass supports shouldn't need supports anymore.

Also modified scad file to better support modifying the magnet sizes.
This one is pre-configured for 0.3 mm magnets.