[IMP] base: no default domain for partner's title

The title field should not have a domain by default.
When a new record is created or the 'is company' field is changed, the onchange_type is triggered to restrict the domain accordingly to is_company field.
When an existing record is modified, there will have no domain on title field. It's not ideal but at least companies will be able to change the title without the need to modify twice the field is_company.
Fixes #1713