Easier to print printable spool holder

I was having issues printing out the original spool holder, so I made this one. Basically, it's thicker which allows for better adhesion to the print bed for printers that aren't fully optimized yet, and I got rid of the rounded ends on the beams. The overhang was causing me problems initially.

This will take longer to print than the old spool holder, but is probably sturdier and is certainly easier to print.

If you need a temporary spool holder for while you print this, I used an old spi