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).

Added the .hgconf file

Updated the NEWS.rst file
Version update in dunder file dunder

Redner varlist substitute get_redner_tmpl_keys func for
retrieving redner templates variables.

Rename "Template" -> "Odoo Template"
Rename "Template + Deserialize" -> "Odoo Template + Eval"

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

Added a custom converter image

This method will be called in ``_render_template`` method to
add additional variables.

Reviewed ir.actions.report and mail template models; Replace
obsolete methode "render_template" by "_render_template"

Retrieve the list of variables present in the template.

Only required for mustache/handlebars template engines.

Following the new functionality (template engine with od+mustache),
this change aims to improve:

* the creation of redner template
* the update of redner template

- 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