Store statistics in a separate page instead of the workflow itself
- advantages:
* smaller workflow instance
- no danger that page is too large for caching, even for large exams.
- smaller objects mean also better performance
* modification date in exam is not modified when statistics
are updated
* easier extensible
- New function WorkflowPage->childpage
easy to use interface for creating child pages
- render_submission=exam_protocol: changed name of
parameter "-form_objs" to "-filter_form_ids", since
form_objs are used typically to keep objects, not ids
- Still to do: policy for inclass-exam-statistics.wf
- Bumped version number to 5.10.1d25
