add prompt confirmation and update carton

lib/pages/faq/faq_edit_page.dart

@@ -127,9 +127,13 @@ class _FAQEditorState extends State<FAQEditor> {
               leading: new IconButton(
                 icon: new Icon(CupertinoIcons.back, color: primaryColor),
                 onPressed: () {
-                  showConfirmDialog(context, "back.button_confirm", () {
+                  if (isDataChanged()) {
+                    showConfirmDialog(context, "back.button_confirm", () {
+                      Navigator.of(context).pop();
+                    });
+                  } else {
                     Navigator.of(context).pop();
-                  });
+                  }
                 },
               ),
               backgroundColor: Colors.white,
@@ -240,4 +244,15 @@ class _FAQEditorState extends State<FAQEditor> {
       });
     }
   }
+
+  isDataChanged() {
+    return _sn.text != "" ||
+        _engQ.text != "" ||
+        _engA.text != "" ||
+        _mmQ.text != "" ||
+        _mmA.text != "" ||
+        _pageLabelEng.text != "" ||
+        _pageLabelMm.text != "" ||
+        _pageLink != info;
+  }
 }