added enchants and custom potions to itemmeta, made fireworks an entity, made damage events only fire once

Adds:
http://redmine.sk89q.com/issues/1551
http://redmine.sk89q.com/issues/2287
http://redmine.sk89q.com/issues/2289
Merge pull request #93 from jb-aero/master

added enchants and custom potions to itemmeta, made fireworks an entity