add missing I18n to permissions page

test plan:
 - run Canvas with LOLCALIZE=1
 - go to Account Settings | Permissions
 - ensure the following fields are localized:
   - "Course Roles" and "Account Roles" tabs
   - "Add Role" button (on both tabs)
   - Contents of the dialog that appears when you press "Add Role"
     (also on both tabs)

fixes CNVS-3118

Change-Id: Ie53ec232df0737149597ae23fe566d9efa241035
Reviewed-on: https://gerrit.instructure.com/34958
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Mark Severson <markse@instructure.com>
QA-Review: Clare Strong <clare@instructure.com>
Product-Review: Jeremy Stanley <jeremy@instructure.com>