Tube holder for Auto-Rewind Spool Holder

For use with [https://www.thingiverse.com/thing:3205383](thing:3205383)

This add-on keeps the PTFE tube above the spool, allowing it to position it very close to the MMU without colliding with the cable bundles of the Prusa i3 MK3.

Edit Nov 11, 2018: Added narrow version tube holder to match narrow filament holder.

Edit Nov 21, 2018: Added V2 versions with some improvements: angled tube guide, easier tube insertion by using a flat-head screwdriver, angled side to avoid spool friction hi