Support German/Austrian version of sixpay/saferpay

[bbb-user-de]

Sixpay/saferpay is now 'worldline'. It might be a good idea to rename the plugin and change the API URL.

For the german and austrain market wordline is not available, but instead https://www.payone.com (cooperation Worldline and DSV-Gruppe (Deutscher Sparkassenverlag)). The Sixpay/saferpay plugin could be cloned, the endpoint behavior can be checked and if necessary adapted (https://explorer.payone.com/?endpoint=CreateHostedCheckout&scenario=Basic).

[ThiefMaster]

If it's the same provider and API, I'd much rather make it configurable enough to work with both. Renaming the default plugin title seems reasonable, changing the plugin/pypi name so much.