The delayed pi-round change can now be triggered via a simple api call.
After the api call a timed task will be started, which executes the
necessary steps for a round change. 

This will result in events being fired at the right time.
Most importantly, this ensures event-specific caching
annotations to work correctly.

getSession throws an HTTP exception, which is not
good style. Additionally, as it calls
getSessionFromKeyword internally -- which has a caching
annotation -- this caching mechanism will not work
because it only works if the method is called
from another object. This is due to the way Spring
is using proxies to intercept the calls.

Events for all learning progress related actions
are generated, like answering a new question.
The event classes are used as a tag to evict
the cache based on the session.

The resource by default now includes the total stats. A user parameter
has been added to request user specific data.

This change intends to restore compatibility with ARSnova Overlay.

#14448

count to NewAnswerEvent websocket broadcast. Task #14471

Updated copyright year and adjusted header format to be consistent over
all files and with other ARSnova projects.

preperation questions. Task #14343

#14099

Had to fix CouchDBDao.getSessionFromId() to implement working permission
evaluation.

This small method had thrown net.sf.json.JSONException wich causes
Spring to send HTTP 405 - Method not allowed and block request.