insert invoice pages

lib/app.dart

@@ -20,6 +20,7 @@ import 'model/chart_model.dart';
 import 'model/device_model.dart';
 import 'model/do_model.dart';
 import 'model/employee_model.dart';
+import 'model/invoice_model.dart';
 import 'model/language_model.dart';
 import 'model/log_model.dart';
 import 'model/main_model.dart';
@@ -66,8 +67,8 @@ class _AppState extends State<App> {
   final PickUpModel pickUpModel = new PickUpModel();
   final ShipmentRateModel shipmentRateModel = new ShipmentRateModel();
   final ShipmentModel shipmentModel = new ShipmentModel();
-  final PackageModel packageModel=new PackageModel();
-
+  final PackageModel packageModel = new PackageModel();
+  final InvoiceModel invoiceModel = new InvoiceModel();
 
   AppTranslationsDelegate _newLocaleDelegate;
 
@@ -102,7 +103,8 @@ class _AppState extends State<App> {
       ..addModel(shipmentRateModel)
       ..addModel(shipmentModel)
       ..addModel(packageModel)
-      ..addModel(shipmentRateModel);
+      ..addModel(shipmentRateModel)
+      ..addModel(invoiceModel);
     this.mainModel.init();
   }
 
@@ -155,6 +157,7 @@ class _AppState extends State<App> {
         ChangeNotifierProvider(builder: (context) => shipmentRateModel),
         ChangeNotifierProvider(builder: (context) => shipmentModel),
         ChangeNotifierProvider(builder: (context) => packageModel),
+        ChangeNotifierProvider(builder: (context) => invoiceModel),
         ChangeNotifierProvider(
           builder: (context) => testModel,
         ),