As a customer/visitor, I want to be able to edit my cart if I change my mind

[Dee-bugg]

• change the quantity of a product in my cart
• remove a product in my cart
• No one else should be able to edit my cart except me

FRONT END

• Add buttons to react component to +/- qty
• Redux action and action creator (or creators?) + reducer case (or cases?)
• Thunk and action handler on react component
• Logic for logged in users
• Logic for guest users

BACK END

• Create express put route for logged in users