This provides smaller and cleaner Interfaces for each context.

remove methods from session controller which are now in its own
controller

All relevant information about users (e.g. session mebership) are
accessible via UserService.
The method IUserService::getCurrentUser provides information about
the actual logged in user. If no user is logged in, this method will
throw a UnauthorizedException which will end up in 401 HTTP error.

Currently, there is an issue with the response. It seems like Spring
is trying to resolve some view, but fails, and then displaying
a message stating POST is not allowed.

/getSkillQuestions/{sessionkey}, by default sort by subject but if
getSkillQuestions/{sessionkey}?sort=text the result will be sorted by
subject and text

The URI to be used contains the session id the question is linked to. If
the resulting question object did not match the given session id an error
HTTP - NOT FOUND will be send. This will also be done if no question was
found.

This layer can be used to create a StubDAO for use with unit tests.

* If a user posts new feedback, while having already posted one, the value
gets updated. This prevents feedback adding up.
* If feedback is too old (10 minutes), it gets removed. For testing
purposes the cleaning routine currently runs every few seconds, and
feedback only lasts a few seconds as well.
* The deleted feedback changes are broadcasted to:
	o All users, if feedback of other users has been deleted.
	o The user whose feedback got deleted.

Currently, this is a huge mess! There are three types of "Session Ids":
* The Socket.IO "session"
* The internal CouchDB session id
* The ARSnova session keyword

A severe clean up is needed before proceeding any further...

This method uses transaction level READ_COMMITTED.

* 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