Fixed#5019 LE cert problem in mirror setups. This patch disables the creation of Let's encrypt SSL certs on mirrored slave servers.

- Fixed #5027 add support for PHP 7.1 and 7.2 on nginx servers in apps vhost.
- suppress some warnings in simplepie.inc.php

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.

Fixed a problem that caused the creation of mysql users to fail. This affected the dev branch only and not the stable 3.1.6 release.

use seperate config for amavis-dkim-config even is the systems uses a monolith config to prevent overwriting the key-config during updates

Fixed #4667 Websites UI / Let's Encrypt :: add Option to allow switching to fullchain.pem in favor of chain.pem