c2b: Export SEPA CustomerToBank statements

The first and currently only C2B application implemented in Lino are payment orders. A payment order is when you ask your bank to perform a payment from one of your accounts to the account of one of your business partners. One payment order may contain more than one such instructions.

There is a DirectPrintAction

A payment order is called "Customer Credit Transfer Initiation" in SEPA and described by pain.001.VAR.VER where VAR is always 001 and VER is 01, 02 or 03.

Lino uses simple Jinja templates files for generating this PAIN XML file.

If I look at code like https://github.com/totaler/sepa/blob/master/sepa/sepa19.py then I feel that no, we are not going to generate the XML file by Python code (using an etree approach) because that would be overkill. We must write test cases which validate the generated XML using lxml and the XSD (code currently in etgen.sepa) but we don't need to do this validity check for each generated document.

pain.001.xml

The template for generating a CCTI is called pain.001.xml and lives in lino_xl/lib/finan/config/finan/PaymentOrder. It currently uses version 02 though 03 seems to be most used nowadays.