Make client protection configurable (#4048)

interface/lib/plugins/sites_web_vhost_domain_plugin.inc.php

interface/web/admin/form/system_config.tform.php

interface/web/admin/lib/lang/ar_system_config.lng

interface/web/admin/lib/lang/bg_system_config.lng

interface/web/admin/lib/lang/br_system_config.lng

interface/web/admin/lib/lang/ca_system_config.lng

interface/web/admin/lib/lang/cz_system_config.lng

interface/web/admin/lib/lang/de_system_config.lng

interface/web/admin/lib/lang/dk_system_config.lng

interface/web/admin/lib/lang/el_system_config.lng

interface/web/admin/lib/lang/en_system_config.lng

interface/web/admin/lib/lang/es_system_config.lng

interface/web/admin/lib/lang/fi_system_config.lng

interface/web/admin/lib/lang/fr_system_config.lng

interface/web/admin/lib/lang/hr_system_config.lng

interface/web/admin/lib/lang/hu_system_config.lng

interface/web/admin/lib/lang/id_system_config.lng

interface/web/admin/lib/lang/it_system_config.lng

interface/web/admin/lib/lang/ja_system_config.lng

interface/web/admin/lib/lang/nl_system_config.lng