update elements and fix some bugs

lib/src/iron-form/iron-form.html

 <!--
 @license
 Copyright (c) 2015 The Polymer Project Authors. All rights reserved.
 This code may only be used under the BSD style license found at http://polymer.github.io/LICENSE.txt
 The complete set of authors may be found at http://polymer.github.io/AUTHORS.txt
 The complete set of contributors may be found at http://polymer.github.io/CONTRIBUTORS.txt
 Code distributed by Google as part of the polymer project is also
 subject to an additional IP rights grant found at http://polymer.github.io/PATENTS.txt
 -->
 
@@ skipping 58 matching lines @@
         type: Boolean,
         value: false
       },
 
       /**
       * Set the withCredentials flag when sending data.
       */
       withCredentials: {
         type: Boolean,
         value: false
+      },
+
+      /**
+      * HTTP request headers to send
+      *
+      * Note: setting a `Content-Type` header here will override the value
+      * specified by the `contentType` property of this element.
+      */
+      headers: {
+        type: Object,
+        value: function() {
+          return {};
+        }
       }
     },
     /**
      * Fired if the form cannot be submitted because it's invalid.
      *
      * @event iron-form-invalid
      */
 
     /**
      * Fired after the form is submitted.
@@ skipping 41 matching lines @@
         this.fire('iron-form-invalid');
         return;
       }
 
       var json = this.serialize();
 
       this._requestBot.url = this.action;
       this._requestBot.method = this.method;
       this._requestBot.contentType = this.contentType;
       this._requestBot.withCredentials = this.withCredentials;
+      this._requestBot.headers = this.headers;
 
       if (this.method.toUpperCase() == 'POST') {
         this._requestBot.body = json;
       } else {
         this._requestBot.params = json;
       }
 
       this._requestBot.generateRequest();
       this.fire('iron-form-submit', json);
     },
@@ skipping 51 matching lines @@
             (el.hasAttribute('is') && json[el.name])) {
           continue;
         }
         addSerializedElement(el);
       }
 
       return json;
     },
 
     _handleFormResponse: function (event) {
-      this.fire('iron-form-response', event.detail.response);
+      this.fire('iron-form-response', event.detail);
     },
 
     _handleFormError: function (event) {
       this.fire('iron-form-error', event.detail);
     },
 
     _registerElement: function(e) {
       e.target._parentForm = this;
       this._customElements.push(e.target);
     },
@@ skipping 63 matching lines @@
       this.appendChild(fakeSubmit);
 
       fakeSubmit.click();
 
       this.removeChild(fakeSubmit);
     }
 
   });
 
 </script>