Implemented #5330 Limit available PHP Handlers globally in ISPConfig UI

install/tpl/system.ini.master

interface/lib/classes/tform_base.inc.php

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

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

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

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

interface/web/admin/templates/server_config_web_edit.htm

interface/web/admin/templates/system_config_sites_edit.htm

interface/web/client/form/client.tform.php

interface/web/client/form/client_template.tform.php

interface/web/client/form/reseller.tform.php

interface/web/sites/form/web_vhost_domain.tform.php