fix account quota XSS vulnerability, fixes CNVS-17656

prevent a malicious course title from XSSing an admin attempting to update
the course's storage quota from the accounts settings Quota tab

test plan:
1. refer to repro steps on CNVS-17656

Change-Id: I3b1dfc5675afc0a1889cb360101c6033cec1517e
Reviewed-on: https://gerrit.instructure.com/46281
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Jeremy Stanley <jeremy@instructure.com>
Product-Review: Jeremy Stanley <jeremy@instructure.com>
QA-Review: Caleb Guanzon <cguanzon@instructure.com>