add filter option for stack-able buff and debuff

[Xiaoyang-Huang]

Due to most 'high dynamic' buffs/debuffs are stack-able
-- like boss debuff on tank.
-- or some charactor need to keep their buff in specific stack, like https://www.wowhead.com/spell=217200/barbed-shot for Hunters

So I think we can add a filter option for stack-able buff/debuff to make them split from main group

Thanks for review the code :)