* 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
