minor fixes in customer-backup-flags integration

Signed-off-by: Michael Kaufmann <d00p@froxlor.org>

lib/tablelisting/admin/tablelisting.customers.php

@@ -23,6 +23,7 @@
  * @license    https://files.froxlor.org/misc/COPYING.txt GPLv2
  */
 
+use Froxlor\Settings;
 use Froxlor\UI\Callbacks\Backup;
 use Froxlor\UI\Callbacks\Customer;
 use Froxlor\UI\Callbacks\Impersonate;