USER STORY: Configure the database models

[PedroMiguelFerreira]

As a developer, I can create the necessary models so that I can set up the project's database

[PedroMiguelFerreira]

• [x] Import the User model
• [x] Create the Customer model
• [x] Create the Product, Order and OrderItem models
• [x] Create the ShippingAddress model
• [x] Migrate the database
• [x] Add all models to admin.py