Admin user develop

To test: 
 * Log in as root. 
 * Go to the admin tab
 * Select root in the tree
 * Check that the administrator box is selected on right-hand side.
 * Select another user e.g. user-1.  Check that the administrator box is NOT selected
 * Expand the Guest group.
 * Select the Guest user. Check that the administrator box is NOT selected

--rebased-from #2054