normalization of nrens including datamigration

normalization of nrens including datamigration The NREN list is hardcoded in the db migration and no new NRENs are made automatically (the db migration crashes if an unknown NREN is found, the excel importers emit a warning and skip the entry). Some NRENs have old or alternative names, which is taken into account in the db migration file and in the publishers helpers.py file.