Option to limit access for remote-user to specified IP(s) / hostname(s) (#4881)

install/sql/incremental/upd_dev_collection.sql

install/sql/ispconfig3.sql

interface/lib/classes/remoting.inc.php

interface/lib/classes/validate_remote_user.inc.php

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

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

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

interface/web/admin/templates/remote_user_edit.htm