Spool holder for MMU2

The spool holders provided with the MMU2 often produce tangles and always introduce a lot of resistance into the filament feed. This filament holder uses a short piece of PTFE tube to avoid loose filament tangling around the spool and uses the axles that come with the MMU2 to make unspooling easy.

When placed above the printer, the split between the MMU2 PTFE tube and the one in the spool holder reliably absorbs the extra filament fed back during unloading.