Monster mana and spellcasting infrastructure changes, Mana Bomb changes (against mobs), new message for ranged mob chance-to-attack.

Design document to come shortly, along with elaborated pull request comment.

Added monster spellbooks, moved mana handling from player/monsters to battler.
Changed how mana bomb affects monsters.
Added a new RangedAttackChance for ranged mobs to use instead of the AdjustedChanceBase which spells use.
Changed shatter out for brittle in avar shamans and ma'xeochicatls.