return purchases screen

lib/screens/purchase.dart

@@ -1,5 +1,6 @@
 import 'package:checker/base/base_screen.dart';
 import 'package:checker/db.dart';
+import 'package:checker/screens/return.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
 import 'dart:convert';
@@ -127,6 +128,16 @@ class PurchaseScreenState<T> extends BaseState<PurchaseScreen> {
     return listView;
   }
 
+  bool showReturnScreen() => true;
+
+  void openReturnScreen() {
+    Future.delayed(const Duration(milliseconds: 200), () {
+      Route route = MaterialPageRoute<String>(builder: (BuildContext context) =>
+        ReturnScreen(helper, app, user['id'], user['bonus']), fullscreenDialog: true);
+      Navigator.push(context, route);
+    });
+  }
+
   getBonusInputField() {
     var bonusTextField = new TextField(
       keyboardType: TextInputType.number,