[Enchantments] Affix Generation

- Starting to build out interfaces and schema for affix generation.
-- Affix entries will be responsible for maintaining spawn requirements (i.e. right now there's only level, but consider time of day, map, active quests, weather, etc).
-- Enchantment entries are defined by their ID, but they're never directly loaded... They still need to be "generated" because they'll randomize their values.
- Affixes can spawn for particular magic types, so the magic type on items has been changed to a guid to represent an ID.
- The item enchantment generator can either spawn enchantments for named items (i.e. prefix/suffix) or random amount.