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)
Fixbug 172426
Fix next and previous buttons to take into account unpublished chapters
Merge branch 'release/candidate' into develop

* release/candidate:
  Fix next and previous buttons to take into account unpublished chapters
  Fixbug 172426