Replaced the use of Json-lib for deserialization by the use of a Map.
This fixes exceptions caused by failed deserializations and is more
consistent with JSON handling of other controllers.
Log messages for easier debugging have been added.

This could be used to send data via websockets without searching
sessionIDs or user tables within ARSnova.

Simply publish an event with ARSnova-sessionKey from within the
application.

Those logging entries are obsolete and only used to grow log files ;-)
Only log log entries if an error occured - not for each event.

countActiveUsers for reportActiveUserCountForSession as it was already
the case for reportSessionDataToClient.
Added check against null for session key in Socket.IO's disconnect
handler.
Logging adjustments for Socket.IO specific code.

certificate errors with SSL.