Universal Spool Holder 24-56mm Remix

This is a minor remix of Robotnik's (http://www.thingiverse.com/thing:127181) original spool holder design.

Modifications made:

A slotted side allowing the entire holder to be forced open slightly to hold two 608 bearings somewhat "locked in".
This slot also increases the flexibility of the holder if spool holder and actual filament spool doesn't meet up perfectly.

Some volume has been added in certain places of the holder since it now has to be a bit stronger than before.