Spool Holder for Filament Shelf

This is a remix of [thing 2685222](https://www.thingiverse.com/thing:2685222) by [rwales](https://www.thingiverse.com/rwales/about). The original was designed to work with version D of [thing 2253244](https://www.thingiverse.com/thing:2253244) by [asteinmark](https://www.thingiverse.com/asteinmark/about). Unfortunately it was too short to work with asteinmark's original shelf design. I have remixed it to be longer and work with the original shelf design. Thanks to asteinmark and rwales for t