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);