Adjustable Printrbot Simple XL Tower Filament Tray Expansion

An adjustable spool holder to swap between different sized filament spools in an instant.

Allows 74mm (Original PrintrBot Spool) to 110mm wide spools to be used.

**Update**
For more stability I added an extension inspired by thing
http://www.thingiverse.com/thing:221509 and
http://www.thingiverse.com/thing:162699

**140308 - Second Update**
Added new parts to allow for spools down to 64mm width (and up to 120mm ;).
The new parts are named '_Narrow' and '_Wide' respectively.