Added rarity filter for Crafting Bases

Added fourth column to crafting_bases.txt for rarity (White, Magic,
Rare, Unique).  Filter is applied as == rather than >= like other
filters.

Fixed handling of multiple items of same name in crafting bases by using
List instead of Dictionary.  This allows for example:
Gold Ring,75,0,White
Gold Ring,75,0,Rare
and have both show up without Magic ones showing up.