Allow guest checkout

[ryan3738]

Allow guest checkout to improve user experience and allow for items to be added to the cart with no user logged in.

[ryan3738]

1. Create a device id cookie for user if they add an item to the cart but are not logged in.
2. When checking out if not logged in ask if they would like to:
   1. Create an account
   2. Sign in
   3. Proceed as a guest
3. If they decide to proceed as a guest
   1. Ask for an email
   2. Create a user with no password using this contact email
   3. Log them in
4. Once logged in link guest cart items with the logged-in user's cart items.
5. Check-out will proceed as normal from this point on.
6. If the user tries to log in or create an account with this email address in the future they will have to perform a password reset and will then have access to this account.

[ryan3738]

Implemented passwordless account sign in to allow for easy account creation