Fix a few sphinx warnings
Update "how to configure shipping" recipe
Rework shipping repository to use a 'methods' attribute

This makes creating simple shipping repositories simpler as you only
need to override the methods attribute.
Update the bankcard type sniffing function
Update payment forms (and tests)

Fields now more self-contained, the bankcard form is much simpler.
Update Bankcard form
Update bankcard model
Add bankcards to admin