Nginx as a reverse proxy

I created a plugin that allows you to use nginx as a reverse proxy.

Merge request for this plugin: !1703

All you need to do is:

1. Change apache port to 6080 for http and 6443 for https.
2. Install Nginx web server
3. Activate the Nginx Reverse Proxy plugin. ln -s /usr/local/ispconfig/server/plugins-available/nginx_reverseproxy_plugin.inc.php /usr/local/ispconfig/server/plugins-enabled/nginx_reverseproxy_plugin.inc.php