PAYMILL: add description when creating preauthorizations

* add description for preauthorizations
* extend supported cards
* add tests for creating transaction and preauthorization with token
@ntalbott I fully agree with you, but here is used PAYMILL's magic [token](https://www.paymill.com/en-gb/documentation-3/reference/api-reference/#create-new-transaction-with). This token is not bound to any account and it is used for test/demo purpose.