Fixes:

• New users can now be assigned required courses even if they're part of a curriculum
• Fixed issue about showing calendar entries for training sessions that belong to archived courses (for administrators)
• Fixed issue about reordering units after deleting a unit with sub-units via content tree in course dashboard
• Fixed issue about reordering units after creating subunit for a unit that already has other subunits
• Fixed issue occurred very rarely in completed tests about duplicated identical entries (by adding a unique constraint for content_progress_ID)