avoid 400 bad request error if ssl is enabled and interface is accessed with http instead of https. Instead redirect to the requested page with https at the beginning of the URL.

According to FS#1982

replaced "listen ... ssl;" through "ssl on;" in nginx (ispconfig.vhost) in case that ssl is used for ispconfig

- Changed FastCGI buffers for ISPConfig nginx vhost because otherwise you get "upstream sent too big header while reading response header from upstream" on OpenSUSE.
- Added 502 error page ("Bad Gateway").
- Added "fastcgi_intercept_errors on;" to nginx vhost template so that ISPConfig's error pages are displayed instead of the default nginx ones.

- Removed ufw configuration from installer to avoid "PHP Notice:  Undefined index: ufw in /tmp/trunk/install/install.php on line 251".
- Changed phpMyAdmin location in ISPConfig nginx vhost to allow phpmyadmin and phpmyadmin/ (with and without trailing slash).