refactored nginx configs

- handle CORS within nginx
- remove allow-headers from CORS
- add custom dynamic error pages
- remove unused fastcgi
- removed OPTIONS backend
- remove previous custom errorDirective
- moved proxy directives to appropiate file

nginx/cors.conf

@@ -0,0 +1,10 @@
+if ($request_method = 'OPTIONS') {
+  add_header 'Access-Control-Allow-Origin' '*';
+  add_header 'Access-Control-Allow-Methods' 'GET, POST, DELETE';
+  # cache CORS for 24 hours
+  add_header 'Access-Control-Max-Age' 86400;
+  # return empty response for preflight
+  add_header 'Content-Type' 'text/plain; charset=UTF-8';
+  add_header 'Content-Length' 0;
+  return 204;
+}