Disable users page for non siteAdmins.
Disable users page for non siteAdmins.

Before, the ensureAdmin was used by the drywall code to lock down
access, but that code was a NOOP that returned true.  This allows admins
to continue to use the site as before, but restrict user management to
siteAdmins.

Issue #263: Admin users and User Administration screen

OpenTechStrategies/smoke-alarm-portal,OpenTechStrategies/smoke-alarm-portal,OpenTechStrategies/smoke-alarm-portal,OpenTechStrategies/smoke-alarm-portal