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.

If some kinds of feedback values do not exist do not throw the exception
NotFoundException. This only indicates, that these values should be '0'
which is the default value.

NotFoundException should only be thrown if the requested session of
feedback does not exist.
Every session has a feedback - sometimes with only 0 values.

questions object

The properties are needed by the client and must not be ignored.

Conflicts:
	src/main/java/de/thm/arsnova/SessionController.java
	src/main/java/de/thm/arsnova/dao/IDatabaseDao.java
	src/main/java/de/thm/arsnova/services/ISessionService.java
	src/main/java/de/thm/arsnova/services/SessionService.java
	src/test/java/de/thm/arsnova/dao/StubDatabaseDao.java

Use this method to implement further checks on session membership.
The old HTTP code assert should never be reached because an
UnauthroizedException should have been thrown first.

This checks if there is a user in current security context. If not, an
UnauthorizedException is thrown which will result in HTTP - 401.

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.

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

doesnt throw exceptions if fields are not set. remove info output

If a session was not found in database this will result in http 404,
if the session is not accessable for the current user the request will
result in http 403.

The old behavior was to check for null. This was the response if the
session was not found or the current user could not access this session
(not owner and inactive sessions). Both ended up with http 404 - not found.

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 method uses the same entity as used for websockets. It needs a valid
session key in request path. This session key MUST match the session key
used in entity to provide semantic URIs