Cart - checkoutpage

[Goodvibesmila]

• [x] Show stripe checkoutpage, when onclick on checkoutbutton in cart
• [x] Create connection between stripe and cart
• [x] create validation for "if logged in"
• [x] autofill from databas if logged in.
• [x] discount code available
• [x] style with css
• [x] commit and push

[Goodvibesmila]

tid för task: 44h 38min (Delat med Cart-task + login som tog några av timmarna)