feature #907 sprint5 :
Refactor the EntityRepository implementation for JPA. The EntityRepository is to represent a repository of business entities.
Because the entities can be an aggregate of data persisted into different data sources (database, JCR, filesystem, ...), it
is expected the repository to take into account of these by using the corresponding data managers.
The JPA EntityManager is one of these managers for the persistence in databases. The EntityRepository implementation for
JPA is just a manager for JPA with additional stuffs for Silverpeas. If the entities are just managed by JPA, then the
repository has just to extend the SilverpeasJpaEntityManager.