Send HTTP UNAUTHORIZED if not logged in into session

These URIs should not be requested if user does not successfully join a
ARSnova session.
Fixes for #6570: Recognize user's role before throwing errors

Renamed TEACHER to SPEAKER to adapt roles to ARSnova client, and
also added some convenience methods for role handling.
Removed obviously unused code
Fix for #5820: Add abstention count to answer stats
Setup UserSessionServices role and user after login

It is required to setup those values after login. Current session
information will be set up after joining a session.
Direct use of userSessionService instead of AOP solution
Save current user into userSessionService after login
Added service methods to check if user is authenticated an in session
Fix for #6584: Store current user in "/whoami" request
Handle empty responses properly
Fixed #6619: Added method to delete all questions of session
Fixed #6646: Disable connector bean

Connector bean has to be disabled because connector could not get any
connection to database server. Connection to database server is
forbidden.
Merge branch 'master' of ssh://scm.thm.de/arsnova/arsnova-war
Bug #6646: Reenabled connector after db connection is enabled again
Removed JH because he left the project several months ago
Removed obsolete Dojo and ST1 implementations for faster builds
Updated outdated README. Unfortunately, the uploaded image is in german.
Updated netty-socketio dependency to release version 1.0.0.
Removed netty dependency. It is only needed by netty-socketio and should
not be required in our POM explicitly.
Updated jackson-databind dependency to version 2.2.2.

These changes hopefully fix the threading problems with redeployment on
Tomcat 7.
Updated netty-socketio dependency to version 1.0.1.
Removed obsolete methods

Feedback is stored in memory on the server, and not inside
CouchDB any more.