LSV and Postfinance Direct Debit file generation

This pull request introduces 2 new features for swiss localization: LSV and Postifnance Direct Debit file generation.
The module uses the "Direct debit order" module (https://github.com/OCA/banking/tree/7.0/account_direct_debit) and the "Banking mandate" module (https://github.com/CompassionCH/banking/tree/7.0-banking-mandates/account_banking_mandate).
The module also uses the changes made in pull request OCA/l10n-switzerland#34 to generate ESR reference if an invoice's associate bank account is LSV-configured.

As the module depends on the banking mandate, which is a new feature in banking-addons, this pull request should not be merged before OCA/banking#27 is merged.
same here