Support CORS requests

[julen]

amaGama currently does not understand CORS requests, and it only provides a workaround via JSONP.

For simple requests, it's straightforward to implement CORS support in the server, and it'd allow to remove the need for JSONP hacks in consumers (mainly Pootle).

[unho]

This is a matter of changing the web server setup. For the record these are the changes we did (copied from http://enable-cors.org/server_nginx.html):

--- nginx.conf
+++ nginx.conf
@@ -80,5 +80,37 @@
+
+                if ($request_method = 'OPTIONS') {
+                    add_header 'Access-Control-Allow-Origin' '*';
+                    #
+                    # Om nom nom cookies
+                    #
+                    add_header 'Access-Control-Allow-Credentials' 'true';
+                    add_header 'Access-Control-Allow-Methods' 'GET, POST, OPTIONS';
+                    #
+                    # Custom headers and headers various browsers *should* be OK with but aren't
+                    #
+                    add_header 'Access-Control-Allow-Headers' 'DNT,X-CustomHeader,Keep-Alive,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type';
+                    #
+                    # Tell client that this pre-flight info is valid for 20 days
+                    #
+                    add_header 'Access-Control-Max-Age' 1728000;
+                    add_header 'Content-Type' 'text/plain charset=UTF-8';
+                    add_header 'Content-Length' 0;
+                    return 204;
+                 }
+                 if ($request_method = 'POST') {
+                    add_header 'Access-Control-Allow-Origin' '*';
+                    add_header 'Access-Control-Allow-Credentials' 'true';
+                    add_header 'Access-Control-Allow-Methods' 'GET, POST, OPTIONS';
+                    add_header 'Access-Control-Allow-Headers' 'DNT,X-CustomHeader,Keep-Alive,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type';
+                 }
+                 if ($request_method = 'GET') {
+                    add_header 'Access-Control-Allow-Origin' '*';
+                    add_header 'Access-Control-Allow-Credentials' 'true';
+                    add_header 'Access-Control-Allow-Methods' 'GET, POST, OPTIONS';
+                    add_header 'Access-Control-Allow-Headers' 'DNT,X-CustomHeader,Keep-Alive,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type';
+                 }
         }
 }