USER STORY: Add checkout views and templates

[johnamdickson]

Epic: Checkout #34

User Story: As a user I can view the cart with items and options to enter details so that I can proceed with completing my order

Acceptance Criteria:

• A form for entering required information for the order object.
• A list of order items presented to the user per site aesthetic.
• User directed to checkout from the cart.

Tasks:

• [x] Implement all required view methods for the checkout app.
• [x] Create template with form for entering user information.
• [x] Wire up secure checkout button in the cart template to access checkout template.

[johnamdickson]

View and template completed for checkout with all required methods. Secure checkout button wired up to access the checkout page.