[FEATURE] Allow more than one company assignment, Fix broken mail sending of unsolicited applications

This ensures the schema is always valid. Otherwise, it could end with a
comma which is seen as invalid schema.

This commit adds a new field and a new record type, the department.
It comes as a replacement for the area text field and allows for
department records to be created. This also introduces a migration
wizard, that can create new departments out of the old area entries.