Replace Hibernate with Eclipselink, model changes + other stuff

- Replace Hibernate with Eclipselink as JPA provider
- Model fix: update RuntimeProperty type
- Model fix: MolgenisUser has two Identifiers (one in superclass MolgenisRole, one though Contact)
- Remove IdentifiableDecorator (didn't do anything)
- OntologyTerm, Institute, Person now extend Characteristic
- Remove index property from Molgenis language
- Use Characteristic.NAME in value converters instead of label value
- Small model cleanups