USER STORY: Set up Checkout app

[johnamdickson]

Epic: Checkout #34

User Story: As a site owner I can ensure items are captured in an order so that customers can complete purchases with all the correct information included.

Acceptance Criteria:

• A checkout app in project.
• A means of capturing order information.
• A means of assigning an order number and totals calculation.

Tasks:

• [x] Create Checkout app
• [x] Create an order class in app models.py file for all items added to cart.
• [x] Create an order line item class to represent each individual item added to cart.
• [x] Add methods to class to append an order number and calculate order total.
• [x] Add order fields and migrate to database.

[johnamdickson]

Checkout app created along with model classes and methods. Migration to db completed.