Implemented: FS#1113 - Force client to use only allowed IPs

- Enabled Security Level (Server Config > Web > Security Level) for nginx.

- Added escapeshellcmd to some paths in nginx_plugin.inc.php.

- Added SEO redirects (both Apache & nginx) to redirect from non-www website to www website or vice versa.
- Introduced placeholder [scheme] for redirect paths for alias and subdomains; will be replaced with http or https, depending on what the visitor uses.

Custom php.ini settings: PHP-FPM might complain about invalid boolean value if you use 0 instead of off, false, or no.

Removed unused database tables: 

DROP TABLE `mail_greylist`;
DROP TABLE `firewall_filter`;
DROP TABLE `firewall_forward`;
DROP TABLE `proxy_reverse`;

- Added tables for web folder protection.

- Fixed FS#1745.

http://bugtracker.ispconfig.org/index.php?do=details&task_id=1681

I've NOT tested this fix, but i think it should be fine.
Someone with Dovecot, please test.

Fixed: PHP notice in tform_actions.inc.php

- Added Limit fields for openvz in the database
- Limited several vm functions to be used by admin only.

Fixed: FS#1709 - Wrong message "Your hard-disk space is going full" in the "Monitor -> Show Disk Usage"

Fixed: FS#1623 - vhost.conf.master placed in /root overrides vhost.conf.master in ispconfig/server/conf

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