Django-thorbanks

* Add support for configuring the sign and verify hash algorithm from Django settings [Thanks mediocrescientist - 29]

- Add support for SHA256 hashing algorithm [Thanks mediocrescientist - 28]

- Django 4.0 compatibility - thanks dmtrm and SirBigG
- test matrix changes

- Add message attribute to AbstractTransaction
- Provide request parameter to transaction_succeeded/transaction_failed
- PaymentRequestBase: Allow usage with existing transaction trough existing_transaction kwarg
- Note: When using this one must also provide the url kwarg (just send the value of pingpack_url argument provided to create_payment_request

- Upgrade cryptography dependency