Heavy duty printable filament spool

This is a 100% printable filament spool based heavily upon randyy's design.

Changes:

Added webbing to arms for strength.
Modified dovetails for better fit (the original required a lot of sanding to get to fit well - for me).
Increased arm thickness for strength.
Increased mount size for strength and more solid connection to MakerBot.
Changed geometry of birdmouth slightly.
Increased size of filament holder so that more filament could be wound on spool.
Added hole in the filament hol