Support CORS requests via framework.js

Adds support for Cross-Origin requests made via framework.js by manually adding the `X-Requested-With: XMLHttpRequest` header required for server-side detection of AJAX requests that is sent on normal Same-Origin AJAX requests but stripped by default by jQuery when making Cross-Origin requests. Note: Request target server still needs to have `Access-Control` headers configured correctly to return a request.

modules/system/assets/js/framework.js

@@ -65,6 +65,7 @@ if (window.jQuery.request !== undefined) {
         }
 
         var requestHeaders = {
+            'X-Requested-With': 'XMLHttpRequest',
             'X-OCTOBER-REQUEST-HANDLER': handler,
             'X-OCTOBER-REQUEST-PARTIALS': this.extractPartials(options.update)
         }