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