Make use of jicson as external dependency

[astirpe]

In module nextcloud_odoo_sync the file jicson.py is actually a copy of the external python library jicson.

Proposed changes:

1. Add jicson in the external_dependencies of the manifest
2. Remove jicson.py file from module
3. Update the code where the jicson is imported, eg. importing it this way:

import logging
_logger = logging.getLogger(__name__)
try:
    import jicson
except ImportError:
    _logger.debug("Cannot `import jicson`.")