eliminate nginx configuration for HTTP_ACCEPT

[revgum]

At the lowest level (Rack?) have the application check public/ns/**/* and the HTTP_ACCEPT for the request to serve a static page rather than have Nginx evaluate the traffic. This update aims at solving the problem where nginx try_files isn't capable of content negotiation.

[revgum]

Issue is referring to nginx configuration:

  #try_files $uri/index.html $uri.html $uri @app;
  # temporary hack to get CVM working with OD
  set $extension "nt";
  if ($http_accept ~ "html"){
    set $extension "html";
  }
  if ($http_accept ~ "ld+json") {
    set $extension "jsonld";
  }
  if ($http_accept ~ "n-triples") {
    set $extension "nt";
  }
  try_files $uri/index.$extension $uri.$extension $uri @app;