Create StripeExternalAccount model and tests #571
Description
Problem
We need to create a StripeExternalAccount model and its tests.
You can only create an external account.
It must have these fields: id_from_stripe, account_id_from_stripe, account_holder_name, account_holder_type, bank_name, country, currency, default_for_currency, fingerprint, last4, routing_number, status
Stripe's docs: https://stripe.com/docs/api#update_account-external_account