USER STORY: Create the static files

[PedroMiguelFerreira]

As a developer, I can configure the static files so that I can use images, CSS and JavaScript on the project

[PedroMiguelFerreira]

• [x] Create the static folder and the css file
• [x] Add STATICFILES_DIRS to settings.py
• [x] Link the static files to store.html
• [x] Add the cart image and link it to store.html to test it