Destroy join table ( checklist ) entries if destroying a rubric
Critical sanity checks added to Criterion ...

1. only one of orange or red flag can be true at a time
2. shortcuts can only be assigned to standard criteria - ie. those created by us
3. if a criterion is changed from standard -> non-standard, then
   it loses its shortcut key
[rubric] Corrected behavioral inconsistencies in Examiner console
 minor corrections in rubric.css to highlight selected criteria