Set tracking mode to COOKIE to prevent session URL rewriting.

There was a bug in the session retrieval code causing an exception.

There was a bug in the session retrieval code causing an exception.

Conflicts:
	src/main/webapp/WEB-INF/spring/spring-main.xml

Conflicts:
	pom.xml

Disabled AOP code executed when joining sessions which caused an
exception because of scoping.

joinSession method since HTTP session is out of scope

Note that this is currently untested. :o

Introduced a new CouchDB view method, and a new field to divide
'skill_questions' into preparation, lecture, and flashcard
variants. The former question type 'flashcard' will be removed
soon.

This is a workaround when a session keyword is entered as a single key

Lots of redundand code deleted thanks to this change

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

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.