change_options set is_template for any owner with is_change; the
"staff only" rule existed only as a disabled checkbox in the UI. A
non-staff owner could mark or unmark templates with a POST, and because a
disabled checkbox is not submitted, a non-staff owner who only edited a
template's title or description silently unmarked it, which lifted the
template-only restrictions.
Only change is_template for superusers and staff (for them an unchecked,
unsubmitted checkbox still means "not a template"); leave it alone for
everyone else.
