Added 2 new command's for Nginx that mimic Apache2's a2ensite and a2dissite command

This add's 2 Nginx command's that act the same as the apache command: a2ensite and a2dissite. You can use them to enable or disable a vhost.

For instance you got a vhost in sites-availabe named "site-one". You can then do the fallowing to enable it: `sudo ngxen site-one` or if you want to disable it `sudo ngxdis site-one`. This basically just add's or delete's symlink's between site-available and site-enabled.

Credits and for more info see: https://blog.kamal.io/post/nginx-apache-like-server-structure/ .