More Magic

Reorganized the magic package, adding a base spell class that the
lightning spell iinherits from. ALso  creating an event hook class, which
makes the player burn in the sunlight (if undead) and take damage from
lightning.

The lightning spell was modified so the damage dealt by the spell can be
easily changed. This was done by creating a magic lightning entity, which
inherits from the Llghtning class but has a base damage, which the event
handler looks for.

Added/fixed create undead spell. Stored the undead status of the player as
NBT data, which is saved with the player. The event hook class looks for
this and burns the player if undead.

Added a summon zombie spell, which summons a zombie in the overworld. The
code was taken from the ItemMonsterPlacer class. The AI needs to be
updated to not attack the player who summoned it.