Renamed `find_field_with_sort_order` to `parse_sorted_field`.

Note that we implemented sorting functionality and added unit tests.

The changes include:

- Creation of a new utility file `utils/sorting.py` implementing sorting
functionalities such as :
`find_field_with_sort_order`,
`parse_fields_with_sort_directions`, and `sortkey`.
- Addition of a new file `tests/test_sorting.py` containing unit tests for
sorting logic.

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

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

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