Adds a role to sidebar buttons on account settings

fixes CNVS-13905

Test Plan:
  - Using NVDA in Firefox go to the account settings page
    (/accounts/##/settings)
  - Using the "B" key the "Add a New Course" and "Add a New
    User" buttons should be recognized.
  - Using the "F" key the same should occur

Change-Id: Ief88cec1f0c12a48ba55ac50614ca83877358a20
Reviewed-on: https://gerrit.instructure.com/40369
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Jeremy Stanley <jeremy@instructure.com>
QA-Review: Clare Strong <clare@instructure.com>
Product-Review: Cosme Salazar <cosme@instructure.com>