private void Button_EditAddressClick(object sender, RoutedEventArgs e)
        {
            AddressItem addressItem = _addressBookViewModel.AddressItems[addressListView.SelectedIndex];

            AddressItem addressItemOld = new AddressItem
                {
                    Name = addressItem.Name,
                    EMailAdress = addressItem.EMailAdress,
                    IsSelected = addressItem.IsSelected,
                };

            AddressItemWindow addressItemWindow = new AddressItemWindow
                {
                    Owner = this,
                    AddressItem = addressItem,
                };

            if (addressItemWindow.ShowDialog() == true)
            {
                _addressBookViewModel.AddressItems[addressListView.SelectedIndex] = addressItemWindow.AddressItem;
            }
            else
            {
                _addressBookViewModel.AddressItems[addressListView.SelectedIndex] = addressItemOld;
            }
            _addressBookViewModel.Save();
        }
        private void Button_AddAddressClick(object sender, RoutedEventArgs e)
        {
            AddressItemWindow addressItemWindow = new AddressItemWindow
            {
                Owner = this,
            };

            if (addressItemWindow.ShowDialog() == true)
            {
                _addressBookViewModel.AddressItems.Add(addressItemWindow.AddressItem);
            }
            _addressBookViewModel.Save();
        }