Accessibility for 'How do I...' menu

fixes CNVS-1328

test plan:
 - With Draft State Off
 - Open the 'How Do I' menu on the Assignment index page
 - The menu should should be accessible
   - specifically the section about creating an Assignment Group
     should be accessible

Change-Id: I7950e8135d500c004dfcf9936d56ee9ed3b86a1f
Reviewed-on: https://gerrit.instructure.com/32431
Tested-by: Jenkins <jenkins@instructure.com>
Product-Review: Aaron Cannon <acannon@instructure.com>
QA-Review: Caleb Guanzon <cguanzon@instructure.com>
Reviewed-by: Liz Abinante <labinante@instructure.com>