Add SEPA fields to member model

The new fields are iban, bic and mandate reference number.
This involves a schema change, so you may have to wipe your db.
Change default choice in AnnouncementForm.

The default choice for the announcement form is now to email only
members who's fees are automatically colected.
Include SEPA fields in csv export.
Include SEPA fields in member web views.
Merge branch 'sepa_support'
Change soup iframe to display local mirror.

1. soup.io will not support HTTPS.
2. Firefox blocks mixed SSL/Non-SSL content by default.

Therefor we fetch a mirror of Metalab's soup every 15 minutes and load
the local copy from the <iframe> on the front page.