ability to reset inventories for a single item#800

add an item field to /reset user inventory and /reset server inventories. inputting an item in this field will make the command solely reset inventories for the specified item.

useful for when a user wants to fully delete an item that has no use to them anymore and thus doesn’t want it staying in inventories. right now, the workarounds are:

1. fully clearing inventories (removes other wanted items);
2. manually removing the item from everyone with an autoresponder (inconvenient for large servers especially since it’s nearly impossible to know every user who has said item);
3. /shop use (inconvenient if you have a lot of the item).