Fixed: FS#2378 - $conf['theme'] value in interface/lib/config.inc.php is overwritten (reset to 'default') on update

Implemented: FS#2283 - Add O option to dovecot transport in postfix master.cf so that X-Original-To: header is added.

Merged revisions 3049-3051,3053-3054,3058,3070,3074-3077,3082,3086-3088,3091-3092,3094-3095 from stable branch.

- Make sure the apps vhost gets configured no matter if the ISPConfig interface is installed or not.

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

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- Fedora installer: create a symlink from /usr/share/phpmyadmin to /usr/share/phpMyAdmin (nginx only).

- OpenSUSE: check if the line "include /etc/nginx/sites-enabled/*.vhost;" exists in /etc/nginx/nginx.conf before it is inserted (installation).

- I had to remove the fail2ban caonfig for now as its incomplete and adds rules for dovecot on courier systems.
It is planned to add a complete fail2ban configuration in one of the next releases.

- 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 support for the /etc/nginx/sites-available and /etc/nginx/sites-enabled directories on Fedora/CentOS to the installer.