converter backport in 2021-06.
In particular, add "HTML + mustache" / "MJML + mustache" instead of just "mustache".

Add constraint on attachment field

Note that it is normally expected that when printing a report from an object,
the created document is saved as an attachment to the object
if the field "Save as attachment prefix" is filled in.

Problem:
This does not work for redner reports (works for QWEB and worked for py3o).

- Bump module version to 13.0.1.0.0
- Remove all the decorators @api.multi, @api.one and so on...
- Update translation files

Render HTML to PDF with weasyprint:

- Use substitution variables in ir.actions.report model
- Send paperformat field info to rednerd when generating a new report PDF
- Refactoring code