GetMinLevel will now return 0 for more cases

For some reason EQ uses 127 (melee classes), 254 (some AAs), and 255
in the class level for spells a class doesn't have
Implemented buff level restrictions

Higher level buffs can't be cast on lower level toons.
The formula was based on information found here: http://samanna.net/eq.general/buffs.shtml
This behavior is controlled by the rule Spells:BuffLevelRestrictions which defaults to true.
Fix some memory leaks in Mob::SpellOnTarget

This should fix the memory leak introduced in the last commit and
a few lingering memory leaks, don't think they should break anything
Changed the MT_Shout to MT_SpellFailure in Mob::SpellOnTarget