Currency Rate Update - Frankfurter

This module extends the currency rate update feature with a new provider option called Frankfurter. It does not add new menus or screens; it plugs into the existing currency rate provider configuration.

• In the currency rate provider settings, the service list now includes "Frankfurter" as a choice.
• When Frankfurter is selected, Odoo asks the Frankfurter service which currencies it supports and only offers those for rate updates.
• When rates are requested, Odoo calls the Frankfurter service for the chosen base currency and the selected currencies, for a single date or a date range, and stores the returned rates by date.
• The list of supported currencies is cached, so it is not downloaded again on every request.
• If the service cannot be reached or returns an error, the user sees a message saying the data could not be fetched and to contact the administrator.

The module touches the currency rate provider model res.currency.rate.provider and relies on the base currency rate update module. It is useful for companies that want free, automatic exchange rates without a paid subscription.