Remove unused (in Tessell & BMP) PropertyGroup.setTouchedOnAll.
Test parent/child model touching in AbstractModelTest.
Revert "Update ListProperty to percolate touched into child models."

This reverts commit ed368dfc3326f97d8d651ed2dd224e5c948b0587.

This logic has janky: external calls to setTouched behaved differently
than internal calls to setTouched, and could result in the external-only
behavior getting skipped if the internal call had already been invoked.

Turns out this functionality already existed in PropertyUtils syncModelsToGroup,
which is less janky and seems to be working fine.