Use an opt-out flow for comments in video, springify notifications and
notifications handlers

The NodeEvaluation makes it difficult to use a course node in the
learning path access concept. So it is refactored to a minimum extent,
so that it can covering the previous functionality.
As a replacement a new security callback and a new tree node type is
introduced.

OO-2967: refactor the list of assessed identities in assessment tools to be delivered by the resource or the course element them self

OO-2897: implement last modification per user role (as participant or as coach), aggregate the values on structure nodes