a bunch of newfiles a11y things acannon suggested in audit

I actually squashed 3 commits into this one
because I figured it would be easer to qa
it all together

first commit:

fixes: CNVS-15604 CNVS-15599 CNVS-15598

see this doc for what to look for and what this fixes:
https://docs.google.com/a/instructure.com/document/d/1XxZXnIeWVJGR6Iko1EuaW6LyiqzEQ-HAucFNq0LQHqs/edit

second commit:

mark newfiles grid up with aria-grid roles

closes: CNVS-15597

test plan:
open new files using a screenreader
the main pane with the grid of files should
function like a table to the screenreader

third commit:

adds screenreader-only feedback and info to
let you know that if you click a col
header it will sort by that col and tells you
if it is sorted ascending or descending

adds a screenreader-only "select all" checkbox
in the header.

Change-Id: I7cfd7133d90079e50cef9c978c2a199fa0530903
Reviewed-on: https://gerrit.instructure.com/41327
Tested-by: Ryan Shaw <ryan@instructure.com>
Reviewed-by: Clay Diffrient <cdiffrient@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
Product-Review: Ryan Shaw <ryan@instructure.com>
QA-Review: Ryan Shaw <ryan@instructure.com>