Cart represents the current items in a user's cart.

Order represents an order in the system.

PaperType represents a type of paper that can be used for printing and its cost.

Print represents a print that a user wants to order.

ShippingDetails represents the shipping details for an order.

TODO: We'll eventually need to support multiple types of shipping profiles (like weight and quantity based).

SupplyCosts represents the costs of supplies for printing.

User represents a user in the system.