Adds an h1 tag to the account settings page

fixes CNVS-13896

test plan:
   - Using NVDA in Firefox go to the account settings page
   - An h1 heading "Account Settings" should be detected.
   - It should not appear on the page.

Change-Id: Iafd81fecbd4e31954f31f39ecd934bd56a06f340
Reviewed-on: https://gerrit.instructure.com/39024
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Jeremy Stanley <jeremy@instructure.com>
QA-Review: Clare Strong <clare@instructure.com>
Product-Review: Matt Fairbourn <mfairbourn@instructure.com>