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-3170: License management: Data model, administration of license types, addition and edition of licenses for learning resources

OO-2891: Update the User only if some attribute values have changed. Wording, testing, mMinor improvements in code redability.