Universal Spool Holder for Prusa i3 MK2S, yes another one...

Lots of these to go around, here's my take.

### Features ###
* Low friction design (bearings)
* Compatible with most spools
* No adjustment needed between different spool widths
* Rollers for 90 mm, 100 mm and 120 mm maximum spool widths included
* Curved flange prevents spool from falling off
* Easy assembly
* Bearing axles reinforced with metal

### Non-printable parts ###
* 4x standard 608Z bearings,
* 4x M3x16 machine screws. Longer ones will work too (they'll stick out insid