This also removes the attr() marking of tests. This can be implemented
in pytest with marking the tests with a custom marker if required.

Before this change, the type of a bankcard would be clobbered by saving
and reloading.

Fixes #1486, #1487

TestCase.assertEquals (note the s at the end) has been deprecated.
The only failing tests remaining are CSV related, which is not
surprising.

Fix to allow users to specify which cards they accept.
By default, this works exactly as it did- i.e., any number
can be entered and only a luhn check is run on it.
Users can now overide this behaviour by passing a list of
accepted cards as a 'types'kwarg to BankcardNumberField,
e.g.
BankcardNumberField(types=[bankcards.VISA, bankcards.VISA_ELECTRON,])

If this is specified, we check that the type of card is one we're
aware of and then that the card number matches the pattern for that
type of card

Fixes #949

@maikhoepfel rewrote the ImproperlyConfigured check using Python's sets.

Conflicts:
	oscar/apps/payment/forms.py

Write a few more tests at the same time.

Useful in templates where the bankcard form is rendered.  Eg:

    {{ bankcard_form.bankcard.obfuscated_number }}

Fields now more self-contained, the bankcard form is much simpler.

This is required for multiprocess testing to work (eg ./runtests.py
--processes=2)