Reuse odoo guess mimetype code and compatibility code between different versions of python-magic.

Also factorize some code and add comment.

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.