FS#3897 - backup - delete unused file (interval = none), fixed mail-backup delete, moved mail-function for failed mounts/umounts

moved dovecot-lmtpd from install/update to server-plugin to prevented dovecot-errors when using dovecot without dovecot-lmtpd

FS#3526 - Add option to disable BIND zone check (the intention for the feature request was more to hide log-messages and not to disable the named-checkzone-call)

- changed language import to use mb_substr

Define bash as a parser, some systems can have "dash" as a "sh" that will end with errors.
# /usr/local/ispconfig/server/cron_daily.sh
[: 10: root: unexpected operator
[: 10: root: unexpected operator

- backported patches

fixes also some misconfiguration under some circonstances

ensure the internal PHP scripts work even if system-wide PHP settings are set that could affect how ISPConfig would work. See FS#3293