add two decimal and add confirm dialog if press back button

lib/pages/rates/custom_editor.dart

@@ -33,7 +33,7 @@ class _CustomEditorState extends State<CustomEditor> {
     if (widget.custom != null) {
       _custom = widget.custom;
       _productController.text = _custom.productType;
-      _feeController.text = _custom.fee.toString();
+      _feeController.text = _custom.fee.toStringAsFixed(2);
     } else {
       _isNew = true;
     }
@@ -63,7 +63,11 @@ class _CustomEditorState extends State<CustomEditor> {
             icon: new Icon(
               CupertinoIcons.back,
             ),
-            onPressed: () => Navigator.of(context).pop(),
+            onPressed: () {
+              showConfirmDialog(context, "back.button_confirm", () {
+                Navigator.of(context).pop();
+              });
+            },
           ),
           backgroundColor: primaryColor,
           title: