WorkflowManager[simple-spring]: fixing JPA issue by using JavaEE default...

... (EJB container) mechanisms for managing the life cycle of SLSBs by using @EJB(mappedName="java:module/XxxService") instead of Spring @Autowired annotation when injecting the bean. Also AbstractEntity was annotated with @MappedSuperclass instead of @Entity. Moreover I added an initial login mechanism which yet lacks some feature, like registration support.