Ability to buy multiple stacks of commands#48

Adding the ability to buy multiple stacks of “commands”

Ex: using a sell wand from a separate plugin inside shopgui+ allowing players to purchase a stack of 64 or 3 stacks of 64.

This suggestion was migrated from old suggestions made at the Discord server.

This feature has been added to ShopGUIPlus:
https://docs.brcdev.net/#/shopgui/shops-items-setup?id=commands