cart functionality

[Dielentheis]

• learn about localstorage
• cart constructor - should mirror cart model - a new cart should be created with a new session and will be stored on localstorage
• when a user logs in, we will also post to a cart route that will add the localstorage cart to the database and be associated with that user. if that user already has a cart, it should just add the items that aren't already present in the user's existing cart.

[Dielentheis]

• cart view should have an order button, when order is placed take cart info and put into an 'order' object to post to an order route and be stored in the DB
• if user logs in and then begins to add items, only use DB storage
• logging in should always check if anything is in the cart and add those items to newly logged in user's cart
• when log out clear the local storage