 Purpose of this mixin is to offer two services

      * compute a sanitized phone number based on _phone_get_number_fields.
        It takes first sanitized value, trying each field returned by the
        method (see ``BaseModel._phone_get_number_fields()´´ for more details
        about the usage of this method);
      * compute blacklist state of records. It is based on phone.blacklist
        model and give an easy-to-use field and API to manipulate blacklisted
        records;

    Main API methods

      * ``_phone_set_blacklisted``: set recordset as blacklisted;
      * ``_phone_reset_blacklisted``: reactivate recordset (even if not blacklisted
        this method can be called safely);
    