Changes

individual costs for NPC commands (#3033)

* Add individual cost option for `/npc cmd cost`

* Add individual experience cost option for `/npc cmd expcost`

* Begin individual item cost impl

Everything is finished except for saving/loading the items. I just need to figure out how to properly save the ItemStacks either by using the DataKey or by somehow figuring out how to use the Persist API

* Add item saving and loading

* Add cost and exp cost to describe message

* Remove debug/todo things

* Make `-1` default to allow for cost-free commands

* Update `describe` function to have proper space alignment

* Change names of cost values

* Update parameter name
 (commit: a2d7284)