This patch uses AbstractController class to add exception handlers
into controllers. These handlers are used to detect some runtime exceptions
which can be thrown in any layer e.g. DAO or service layer.
They recognize NotFoundException and ForbiddenException. Test classes are
able to check if any of these exceptions are thrown during runtime.

* Added session controller with method to get session by id
* Created session class to be used as entity object
* Created session service class and interface
* Added content negotiation view resolver to map entity objects to JSON