Add support for JPA annotations

It looks as though OpenMRS may be able to support JPA annotations in entities by getting HibernateSessionFactoryBean to extend AnnotationSessionFactoryBean.

Modules may also need to specify either annotated classes or packages that would be scanned to pick up entities.

Some initial discussion on the OpenMRS developer mailing list:
https://groups.google.com/a/openmrs.org/d/topic/dev/b_B_rJ85Ldo/discussion