Back corner spool mount for Lack Enclosure

This replaces the back right top corner Lack Enclosure piece with one that includes a sturdy modular spool holder bracket. This works really well with a Mini, leaving space to swap spools without getting in the way and directs the filament on a clean path to the extruder (feed it over, not under the spool). YMMV for any larger printer. The modular bracket design is based on the Filler spool holder from Thingiverse. I've included a modified version of the actual holder which is 1) more compact but still large enough for most brand 1kg spools and 2) has slightly more aggressive end stops on the roller so the spool doesn't migrate off. It should work fine with the original as well. See the original for links to purchase the 608 bearings. The usual supports for that piece plus paint some on the underside of the bracket to either side of the slot.