Add item selling functionality

[tagniam]

The game currently allows the player to buy items from Jeremy's Tool Store, but the player cannot sell any items from their inventory to the store. We'd like to implement selling functionality in Jeremy's Tool Store.

The player should be able to sell items at the same price they can be bought, for example since 1 bomb from the store costs 100 coins, the player should be able to sell 1 bomb from their invenyory for 100 coins.

[JerBast]

I would like to work on this, if possible.

[tagniam]

@JerBast Sure 👍