Merge branch 'stable-3.1'

install/sql/incremental/upd_dev_collection.sql

install/sql/ispconfig3.sql

install/tpl/mysql-virtual_sender_login_maps.cf.master

interface/lib/classes/quota_lib.inc.php

interface/lib/classes/remote.d/sites.inc.php

interface/web/mail/form/mail_alias.tform.php

interface/web/mail/form/mail_forward.tform.php

interface/web/mail/lib/lang/de_mail_alias.lng

interface/web/mail/lib/lang/de_mail_forward.lng

interface/web/mail/lib/lang/en_mail_alias.lng

interface/web/mail/lib/lang/en_mail_forward.lng

interface/web/mail/templates/mail_alias_edit.htm

interface/web/mail/templates/mail_forward_edit.htm

interface/web/sites/ftp_sites_stats.php

interface/web/sites/lib/lang/en_ftp_sites_stats_list.lng

interface/web/sites/lib/lang/fr_ftp_sites_stats_list.lng

interface/web/sites/list/ftp_sites_stats.list.php

interface/web/sites/templates/ftp_sites_stats_list.htm

server/lib/classes/cron.d/200-ftplogfiles.inc.php