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.

& latest xcg/templates/odoo_module.

Similar in the 13.0 branch: 7cc12fb73390

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