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.

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

It seems that Jetty provides "com.fasterxml.jackson.databind.JsonNode"
in any way but Tomcat does not.

So we have to include the package containing this class in our Maven
configuration.

We seriously have to check if ARSnova runs on our main target platform,
not only our private developer platform! My be our developer platform
should be the main target platform?

LoginControllerTest::testUser() is still included as comment. This test
must be reenabled in near future.

Finally the security implementation needs much more testing!

Old tests are ignored because they allways fail with unknown reason.
The new tests are very simple and there is a lot of work to be done to
have a fully tested application.

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

* @ResponseBody Annotation for JSON Response
* Old ARSnova Servlet does nothing
* New Spring Servlet loads Beans, Services, Security and SocketServer
* One Property Loader which is used in XML Spring Configuration and with
@Value Annotation

With this configuration both
 - spring security setup
 - bean properties
will be set to values defined in /etc/arsnova/arsnova.properties.

Admins ARE REQUIERED to create production settings file by given example
in /etc/arsnova.