Add a test of the semantics of About items
Add a test of the semantics of About items

These are XBlocks that are detached (not part of the course content hierarchy),
and are also DIRECT_ONLY_CATEGORIES (meaning they are always autopublished).

https://openedx.atlassian.net/browse/PLAT-858 identifies a bug
where an About item isn't correctly deleted in SplitDraft, and this test
reproduces that case.

bmedx/modulestore,bmedx/modulestore,bmedx/modulestore