Prevent from selling items in set or above some iLvl

[lukaszsmoczynski]

Because of mythic gear system it is possible to mark item from regular mythic dungeon (let's say from WoD expansion) but that also makes my current high-end item from m20 key to be marked to sell.

I'd suggest adding option to either prevent selling items that are in any set made by user or that are above certain iLvl to distinguish low iLvl junk from currently used items.