template upload.

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).

Rework on relations converters
Remove deprecated field (ie: deserialize)
Use converter on mail template model
Updated the french translations

- 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

Add rednerd template management API to let the user save templates
for later use with the rendering api:

- POST: /api/v1/template/{account}
- PUT: /api/v1/template/{account}/{name}
- DELELTE: /api/v1/template/{account}/{name}

Render a custom template:

- POST: /api/v1/render