DBUtil: utility functions for service classes using JPA
ConferenceService: use DBUtil

Use DBUtil also in unit test
ConferenceServiceTest: remove println() calls
Model: change relationships from List to Set
JPA: switch from hibernate to eclipse link
ConferenceService: implement get() and create()

Unit test for new methods
Build: remove unused dependencies

- remove hibernate
- remove javaJpa
Merge: resolve conflicts

Conflicts:
	app/service/ConferenceService.scala
	test/service/ConferenceServiceTest.scala