[Payment Method] Bank transfer

I expect that when downloading an curated elementary OS using AppCenter, I will have a chance to support the project financially, even if I don't want to support/trust the big proprietary vendors like PayPal or Stripe.

Anonymous payment methods would also be desirable for people for whom this is important for certain reasons.

See https://github.com/elementary/website/issues/2160 for reference

---
Want to back this issue? **[Post a bounty on it!](https://www.bountysource.com/issues/70280257-payment-method-bank-transfer?utm_campaign=plugin&utm_content=tracker%2F57667267&utm_medium=issues&utm_source=github)** We accept bounties via [Bountysource](https://www.bountysource.com/?utm_campaign=plugin&utm_content=tracker%2F57667267&utm_medium=issues&utm_source=github).