added student name and grade status to live region

student name is announced after clicking next/prev buttons, or grading assigment

fixes CNVS-15546

test plan:
- go to speedgrader with voiceover enabled
- click on next button and previous buttons
- name and grade status of student should be announced
- add a grade to current assignment
- name and grade should be announced
- repeat for removing grade
- repeat process with student names hidden to ensure names remain anonymous

Change-Id: I8c4c7d4acad1009e74b2df3d05c9fcc84e86e7ab
Reviewed-on: https://gerrit.instructure.com/42191
QA-Review: Sean Lewis <slewis@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Simon Williams <simon@instructure.com>
Product-Review: Aaron Cannon <acannon@instructure.com>