In Model converter, also validate messages in ``message_to_odoo``.

Model converter argument changed, `__type__` is now the last argument and is optional. It is expected not to be used
anymore.
Added possible_datatypes property and odoo_datatype on Converter. Defaults to empty set and None.
On Model, it can be set.

Replace generic exceptions.

to facilitate expression error handling

📚 Use ©

Change get__type__ to return a set of values.
It is defined at the Converter level despite only returning a value for a small number of Converters but it simplifies the code using it to do so that way.

Validation and validator can be set on converters after initialization. Only some converter makes use of those values.
This makes the message_to_odoo_validate method unnecessary, that’s why it has been removed.

📝 Add tests, correct code so test passes.
Fix issues with some converter.