Core/Spells: Anti-Magic shell should give immunity to all spells that belong to SPELL_SCHOOL_MASK_MAGIC regardless of dispel type

https://github.com/TrinityCore/TrinityCore/issues/877
https://github.com/TrinityCore/TrinityCore/issues/2353
https://github.com/TrinityCore/TrinityCore/issues/2408 (part of it)