let site admin see hidden features in any context

test plan:
 - a site admin user should be able to see the hidden
   lor_for_user feature in User settings
 - a non-site admin user should not be able to see it,
   unless a site admin user has already set it for the user

fixes CNVS-14779

Change-Id: If9a42546b209607b8728ecdb682ad0aeefe99136
Reviewed-on: https://gerrit.instructure.com/39292
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: James Williams  <jamesw@instructure.com>
Product-Review: Bracken Mosbacker <bracken@instructure.com>
QA-Review: Clare Strong <clare@instructure.com>