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.

- Fixed a bug in server settings rescue page.

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- Removed ufw firewall tab.

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

Fixed bug that caused the wrong list to be loaded when the return key was pressed in a search text field of a list.