fixed small bug in mail-backup-cron

Fixed error in Mail-Backup-Cron-Task (created file /dev/nul - missing l)

additional added mail_backup to webspace-quota if mail and webdomain are on the same server
changed backup-filesize from formated string to byte-count, because of low-level-remote functions

Removed possibility of reinstalling Instances

- Added HHVM to "Default PHP Handler" field (server configuration).
- Fixed "Unable to load the server configuration from database." error when running server.sh.
- Fixed Javascript (accordions weren't working anymore, directive snippets and other placeholders couldn't be added anymore).

- Fixed: FS#3710 - Bug with PHP-FPM configuration since 3.0.5.4 Patch 4
- Fixed wrong function calls in system lib.

- Fixed a problem with restart of services due to the fact that Ubuntu has upstart and systemd installed, but only upstart is working without errors.

- Added warning in the interface when a path for a shelluser is set that is outside of the website docroot.
- Added security settings feature to allow the root user of a server to control most aspects of whet the admin user of the controlpanel is allowed to do in system settings. This is especially useful for managed severs where the ispconfig admin user and the root user of the server are different persons.