Add product to shopping cart

[ghost]

Ability to add products in CLI tool where the User can register a Customer, view/add products, add payment, and complete an order.

Context

Assuming a Customer account has been created (see issue #3), and the user has selected an active customer from Main menu(see issue #5), the user will be able to add products to their shopping cart.

Expected Behavior

On start, Main menu option4 is "Add product to shopping cart". When Menu option no.4 is selected, the user is shown a product list from which to select a product to add to their shopping cart. The user may only select one product at a time. Until the user selects the last option on the product list, which will be "Return to main menu", they will return to the product list each time a product is selected.

If the user selects menu option4 but has not selected an active customer (issue #5) from existing customer accounts
(issue #3), then the user will be redirected to the Main menu with a prompt to Select an active customer.

(Each product purchase will add a row to the OrderProduct table. If a product hasn't yet been purchased by any user, the initial purchase will necessarily add the product to the Product Popularity report (see issue #8).)