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/error_map.conf

@@ -0,0 +1,15 @@
+map $status $status_text {
+  400 'Bad Request';
+  401 'Unauthorized';
+  403 'Forbidden';
+  404 'Not Found';
+  405 'Method Not Allowed';
+  408 'Request Timeout';
+  409 'Conflict';
+  429 'Too Many Requests';
+  500 'Internal Server Error';
+  502 'Bad Gateway';
+  503 'Service Unavailable';
+  504 'Gateway Timeout';
+  505 'HTTP Version Not Supported';
+}