bug #4361 : An error is raised when a position on the Pdc is set with the same values of a position of another predefined classification

When predefining a classification on the PdC for a topic in a Kmelia instance, if a position contains one or more same values of a position in an already existing predefined classification (attached to another topic of the same or of another Kmelia instance), an error is raised and the user receives an Internal Server Error (HTTP status 500).

Now the existence of axis values are checked before saving a position on the PdC for a predefined classification; the JPA implementation by hibernate doesn't seem to respect correctly the JPA specification with the 'persist' cascading (with the persist cascading in a relationship, the related entities are saved only if they don't exist. Here Hibernate want absolutly create them whatever they already exist or not)