Fix #168716 (wrong behaviour for disabled chapters and unified urls)
Removed subchapters when chapter is disabled
Fix #167797 (impossibility to duplicate a lesson into a personnal workspace)
Fix crash when creating a lesson
Merge branch 'develop' into release/candidate

* develop:
  Fix #167797 (impossibility to duplicate a lesson into a personnal workspace) Fix crash when creating a lesson
  Removed subchapters when chapter is disabled
  Fix #168716 (wrong behaviour for disabled chapters and unified urls)