CQS: better page headings

- there's an H1 for the page that reads "Quiz Statistics" visible only
  to screen-reader
- rest of the headings are of levels H2 and H3

Closes CNVS-16312

Change-Id: I35c7d06f3ef9f9ffd59f7eaa1840173b1a1ee58a
Reviewed-on: https://gerrit.instructure.com/42953
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Derek DeVries <ddevries@instructure.com>
QA-Review: Trevor deHaan <tdehaan@instructure.com>
Product-Review: Ahmad Amireh <ahmad@instructure.com>