At least caching of learning progress responses
did not work since commit a59eb75f on March, 6th.

While the exact origin of this problem is unclear,
it seemed like Spring was creating more than one
databaseDao bean. One of these beans had no
working caching annotations.

These events add more detail about what specific
action just happened.

Unlock is a better representation because this event only
occurs when multiple questions are published. 'New' should
only be used when questions are created.

Task #15666
Task #15693

Just for consistency.

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. 

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.