private void BtnSave_Click(object sender, RoutedEventArgs e)
        {
            var user = new User
            {
                Name = InputUsername.Text,
                HourlyRate = float.Parse(HourlyRateBox.Text),
                HolidayHours = float.Parse(HolidayVacancyHourBox.Text),
                VacancyHours = float.Parse(HolidayVacancyHourBox.Text)
            };

            if (user.Save())
                this.Close();
        }