Error if DateNormalizer produce "Unknown-Format"

[ncarboni]

When using DateNormalizer, if a string it is not correctly transformed, it should print an error.

Example: the date

<Datation_De_DateCreation_ISO>-12900-01-01</Datation_De_DateCreation_ISO>

if transformed in xsd:dateTime has the following output:

<example/951478/creation/time> <http://www.cidoc-crm.org/cidoc-crm/P81a_end_of_the_begin> "Unknown-Format"^^<http://www.w3.org/2001/XMLSchema#dateTime> .

while it is the expected behaviour, it would be helpful if an error is printed/provided to the users