Handle Buffs/Debuffs before start channeling

Gives the possibility to modify channeling time depending on
buffs/debuffs/diminishing returns
Immune message if mob has 3 diminishing returns

Returns a immune message to the client if the spell fails because of 3x
diminishing return
Revert "Fixed SMSG_SPELL_FAILED_OTHER"

This reverts commit c4da9d5e3adf857ac6a5dd6c2c322b09151468c2.