rename received_by_notify to accepted

accepted is nice since it both implies that things look good, while
not being commital about next steps.

tests/app/test_model.py

@@ -116,8 +116,8 @@ def test_notification_for_csv_returns_correct_job_row_number(notify_db, notify_d
     ('sms', 'temporary-failure', 'Phone not accepting messages right now'),
     ('sms', 'permanent-failure', 'Phone number doesn’t exist'),
     ('sms', 'sent', 'Sent internationally'),
-    ('letter', 'created', 'Received by Notify'),
-    ('letter', 'sending', 'Received by Notify'),
+    ('letter', 'created', 'Accepted'),
+    ('letter', 'sending', 'Accepted'),
     ('letter', 'technical-failure', 'Technical failure')
 ])
 def test_notification_for_csv_returns_formatted_status(

tests/app/v2/notifications/test_get_notifications.py

@@ -573,7 +573,7 @@ def test_get_all_notifications_renames_letter_statuses(client, sample_letter_not
         if noti['type'] == 'sms':
             assert noti['status'] == 'created'
         elif noti['type'] == 'letter':
-            assert noti['status'] == 'received_by_notify'
+            assert noti['status'] == 'accepted'
         else:
             pytest.fail()
 
@@ -588,4 +588,4 @@ def test_get_notifications_renames_letter_statuses(client, sample_letter_notific
     json_response = json.loads(response.get_data(as_text=True))
     assert response.status_code == 200
 
-    assert json_response['status'] == 'received_by_notify'
+    assert json_response['status'] == 'accepted'