Lich King heroic version fix

Sorry for that earlier commit I admit i fucked sth up... it should be all ok now. This should make the Val'kyrs immune to deathgrip effects, it decreases their fly height (still in melee range), also I slowed down Wicked Spirits and Spirit Bombs in Frostmourne room. The Spirit Bombs now have also a 3 sec explosion delay as it should be. 

PS: The part which makes Val'kyr to not drop players after stuns/charge effects is not mine i just implemented it and saw it works. Originaly it comes from here: https://github.com/TrinityCore/TrinityCore/issues/7266