Refresh, update, and document Nginx configuration

Thanks to some excellent reading provided by H5BP in their [nginx server configs repo](https://github.com/h5bp/server-configs-nginx/blob/master/nginx.conf), I was able to clarify and better document a few of the settings in our Nginx configuration as well as add a couple other directives.

Things seem to be working fine currently, please open up an issue if you start noticing weird Nginx behavior