kfet -- Create initial statement on checkout save

- Why? Because it should be the actual behavior.
- To allow using arithmetic operations with values of DecimalField when
object are not retrieved from DB, some strings are replaced by Decimal
or int.
If you wonder why it's not automatically done, see:
https://code.djangoproject.com/ticket/27825

kfet/tests/test_views.py

@@ -746,12 +746,16 @@ class CheckoutReadViewTests(ViewTestCaseMixin, TestCase):
 
     def setUp(self):
         super().setUp()
-        self.checkout = Checkout.objects.create(
-            name='Checkout',
-            created_by=self.accounts['team'],
-            valid_from=self.now,
-            valid_to=self.now + timedelta(days=5),
-        )
+
+        with mock.patch('django.utils.timezone.now') as mock_now:
+            mock_now.return_value = self.now
+
+            self.checkout = Checkout.objects.create(
+                name='Checkout', balance=Decimal('10'),
+                created_by=self.accounts['team'],
+                valid_from=self.now,
+                valid_to=self.now + timedelta(days=1),
+            )
 
     def test_ok(self):
         r = self.client.get(self.url)
@@ -794,7 +798,7 @@ class CheckoutUpdateViewTests(ViewTestCaseMixin, TestCase):
             name='Checkout',
             valid_from=self.now,
             valid_to=self.now + timedelta(days=5),
-            balance='3.14',
+            balance=Decimal('3.14'),
             is_protected=False,
             created_by=self.accounts['team'],
         )
@@ -864,6 +868,7 @@ class CheckoutStatementListViewTests(ViewTestCaseMixin, TestCase):
         self.assertQuerysetEqual(
             r.context['checkoutstatements'],
             map(repr, expected_statements),
+            ordered=False,
         )