and make changes to mysql users in the mysql plugin module.

Refs: 1722

- Fixed UTF-8 support in email function.

- Installer adds Apache and nginx user to ispapps group.
- Installer makes sure that /var/www/apps has 755 permissions.

- Added PHP-FPM pm settings (pm.max_children, pm.start_servers, pm.min_spare_servers, pm.max_spare_servers) to the "Options" tab of a website.

- Installer adds ispconfig user to Apache group on Fedora/CentOS so that nginx/PHP-FPM can access /etc/squirrelmail and serve SquirrelMail for the ISPConfig vhost.
- Added session.save_path and upload_tmp_dir settings to the PHP-FPM pool definitions.

- Added SNI config field in sysetm > server config > web.

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.