Write default values to a config file. If another config file
    already exists, back it up before replacing it with the new file.

    :param config_file: `pathlib.Path` object. Path to config file.
    :return: `ConfigParser` object with the values loaded.

def _use_default(config_file):
    """Write default values to a config file. If another config file
    already exists, back it up before replacing it with the new file.

    :param config_file: `pathlib.Path` object. Path to config file.
    :return: `ConfigParser` object with the values loaded.
    """
    default_config = OrderedDict((
        (
            'gui',
            OrderedDict(
                (
                    ('message_duration', 5),
                    ('gui_welcome_label', 'Welcome to the STEM Learning Center!'),
                    ('full_user_names', True),
                    ('large_font_size', 30),
                    ('medium_font_size', 18),
                    ('small_font_size', 15),
                    ('tiny_font_size', 10),
                    ('max_input_length', 9),
                )
            ),
        ),
    ))

    parser = configparser.ConfigParser()
    parser.read_dict(default_config)

    if config_file.exists():
        backup = config_file.with_suffix('.bak')
        os.rename(str(config_file), str(backup))
        logger.info('{} moved to {}.'.format(config_file, backup))

    with config_file.open('w') as f:
        parser.write(f)

    logger.info('Default config file created.')

    return parser