Several fixes, see detailed log.

Model:
- Fixed Participant not having a primary key
- Fixed getEventsForUser, getInvitesForUser (and some others)
- Removed Queries from Comment

Controllers:
- Made all Queries (non save/update) Transactional
- Fixes for the above change

Tests:
- Changed test cases to reflect above changes

Other:
- Fixed database path in hibernate.cfg.xml