Fix failing grade label being editable but not saved.

The root cause was that `failBar` was a string on line 173. Thus, wrapping it with `$` created a new DOM element, set its child span's `contenteditable` to `false`, and promptly threw it away and appended a new element to `gradelist` on 174 (with `contenteditable` as it was in the template). @cahrens, can you confirm the fix?