[ADD] backport sepa direct debit

This is a backport of account_banking_pain_base, account_banking_sepa_direct_debit and account_banking_payment_export. Creating mandates and exporting payment order to PAIN works, but up to now I couldn't look into possible side effects of installing account_banking_payment_export
This should be enclosed in a try to avoid a crash in server startup if library is not present, or move it to the method where is used (and thus only used if module is installed).