TUSH spool holder base frame

Thanks to filamentry for the well designed original TUSH, and to Duphill for for the simple, effective support for various spool sizes.

This remix expands on Duphill's design to create a single unit with the two pieces set the precise distance apart to fit the original TUSH assemblies snugly with no extra play. They nonetheless remain easily movable from one slot to another for different spool sizes without having to mess with aligning loose parts.

This is meant to be used with the original TUSH. Remixes that do not change its base dimensions should also work.

v2: added another slot to frame to accommodate more possible sizes.