Fix how barriers work please

[CaptainLagbeard]

Sage and Scholar barriers shouldn't overwrite each other, they should be allowed to be stacked from different healers much like Regen effects can be stacked.

In End-game content it doesn't matter that much, as groups need to be pre-made you won't get overlap on the healers, but in random queuing for Normal difficulty raids, it actually hurts the group when you get 2 SGE, 2 SCH or one of both since they're going to mess up each others shields...