Core/Spells: Implement Periodic mechanics

Change behaviour of single target periodic aura ticks to be more blizzlike
Also add some missing handling of SPELL_AURA_MOD_CREATURE_AOE_DAMAGE_AVOIDANCE
Fixes Deep wounds and Chimera Shot Serpent
Remove an ancient hack with Drain Soul, spell id 100001 can now be deleted from spell_dbc table
Allows Rolling dot mechanics and allows DK's to roll diseases with pestilence,
see link for info:

http://forums.elitistjerks.com/topic/82503-frost-dps-in-333this-will-be-a-day-long-remembered/page-88