Complete buy/sell functionality for the market and housing screens

[deandrebaker]

When a user clicks on the Contact Seller button, the user should be added to the list of contacted sellers on either the ad, listing, or roommate post. We need to add endpoints on the api to support this, then we need to hook up the components in the front-end to these endpoints.

Also, after they are added to the list of contacted sellers, a new chat room is created between the seller and potential buyer. We need to create a new view for these special rooms between potential buyers and sellers.

Lastly, we need to add endpoints and hook up the functionality for confirming that an item is sold in the chat room.

[deandrebaker]

Backend tickets have been made.