Spell overhaul - move item enchantments to new itemench class.

Part of overall spell overhauls. Split off spells that primarily affect/are cast on items to a new subclass of Spell. 

Spell changes:
Artifice is changed to only affect weapons/armor, enchantment time lowered (see #493). 
Enchant weapon focus time lowered to 15 seconds, reagents lowered to 2 elders/1 tooth.
Glow reagents lowered to 1 mushroom/1 elder.
Holy weapon focus time lowered to 15 seconds, reagents lowered to 2 fairy wings/1 tooth.
Shroud focus time lowered to 8 seconds, reagents lowered to 2 mushrooms/2 elders.
Unholy weapon focus time lowered to 15 seconds, reagents lowered to 2 fairy wings/1 tooth.

Spell descriptions updated with reagent cost.