Delete no-longer existing lessons

added part::backend type::bug labels

Nope. This will invalidate all class register entries for previously existing lessons. We cannot do that. Lesosns are one of the data types that must never be deleted.

Please us edjango-reversion to do a soft-delete.

You can even recover lessons that are reintroduced in an import this way.

marked as a Work In Progress

added 8 commits

• 6539d3c7...a3c3f678 - 6 commits from branch master
• c20a946a - Merge branch 'master' into fix/delete-old-lessons
• f14e7d94 - Use django-reversion to delete lessons

Compare with previous version

Please review again, @nik .

unmarked as a Work In Progress

resolved all threads

merged

mentioned in commit 3eaec0a7