Universal filament spool holder

This is a filament spool holder based on MrMdR's design. Main changes:
- it requires less filament than the original
- it has an inset for the bearing so that it doesn't accidentally gets stuck and also leaves about 2mm more room for the spool's edge
- it has been recreated in Solidworks. The SDLPART is provided, feel free to change the parameters around!

You will need two of these to hold a single pool of filament. The holder has been designed for M4 bolts and 624 bearings (4mm inner diameter, 5mm thickness).