Create a Game Power Up Shop

[kifung]

Make a game power up shop where the player can use game currency to purchase different power ups. The purchased items are stored in the inventory and can are used in the game. The store can also have a limited supply per power up that respawn in a time limit. This issue is tied to #23 #96.
Estimated ~550 points?

[Sierrasch]

#23 needs to be done first