Update NGINX config for Ajenti V

Ajenti V currently uses a not so accepted NGINX configuration (regarding the main config files).

My suggestion is to use the standard definition:
- fastcgi.conf and fastcgi_params in /etc/nginx instead of fcgi.conf
- Use original NGINX configuration wherever possible
- Use original configurations for all included elements (php5, fcgi, mysql)
- Use original php5-fpm socket