Implement useItem

[A554551N]

useItem is a big milestone for the project. It should:

• take in the id number of an item
• check the ID against the user's inventory (to make sure they have at least one)
• perform whatever logical action is required
• reduce the quantity of the item in their inventory
• update the owned_items db with the newly reduced quantity

[A554551N]

useItem is complete and implemented as part of 0.4.0