global option to enable pagespeed with nginx - allows to enable pagespeed even if no webserver-config is selected

- fixed backups not downloadable on multiserver slave, fixes #4973

- fixed accidently deleting mysql r/o user completely when it is removed from a single database, fixes #4963

Fix bug where in a multiserver setup, deleting a backup will not remove its details from the master database as well.

Fix typo in parent user related variable when creating new jailkit shell user. This bug was interfering with the correct functioning of the plugin.

every cron execution. The logfile can be disabled by using -NoLog