Kit core list class.
It is available only on Snipe Kit server.
add (itemID:Int, ?amount:Int):Item
Adds an item with a given item ID and amount to this list. If the item already exists and has "amount" field defined, it is increased instead. If it does not exist, new item is created.
Parameters:
itemID Item ID of the list item (not index!).
amount (optional) Item amount. Defaults to 1.
Returns:
Item instance that was created or updated.