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

- Fastcgi: delete .php-fcgi-starter directory if another PHP mode is used.

- nginx: merge function: default action is now to replace older locations in the nginx vhost configuration; a merge  instead of a replacement can be achieved by putting the string "##merge##" (without quotes) at the end of the most recent location line (e.g. "location ~ \.php$ { ##merge##").

- Improved support for multiple PHP versions. Additional PHP versions have now their own form and database table.

- Added "actions" framework in server to replace the functions provided by the core modules
- Moved system update function from remoteactins core module to software update plugin.

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.