add pt-BR translation

closes CNVS-12126

test plan
 - change your user settings to Português do Brasil
   and verify that the new translations appear
   properly

Change-Id: I3be754708aaa53eb5af09a600489f8eb341527d5
Reviewed-on: https://gerrit.instructure.com/32619
Reviewed-by: Brian Palmer <brianp@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Jeremy Putnam <jeremyp@instructure.com>
Product-Review: Rob Orton <rob@instructure.com>