Make client protection configurable (#4048)

interface/lib/plugins/sites_web_vhost_domain_plugin.inc.php

interface/lib/plugins/vm_openvz_plugin.inc.php

interface/web/client/domain_edit.php

interface/web/mail/mail_mailinglist_edit.php

interface/web/mail/xmpp_domain_edit.php

interface/web/sites/web_vhost_domain_edit.php