webui: hide empty fields and sections
Hide widgets without a value. Must be explicitly turned on. In widget by
`hidden_if_empty` flag. Or globally by `hide_empty_widgets` flag. Global
hiding can be individually turned off by `ignore_empty_hiding` flag.
https://fedorahosted.org/freeipa/ticket/4402
Reviewed-By: Endi Sukma Dewata <edewata@redhat.com>