private void StoreNumber_TextChanged(object sender, TextChangedEventArgs e)
        {
            //When the text changes check to make sure that we have a number not letters.
            if (IsTextAllowed(sender.ToString()))
            {
                StoreCheckInt.Foreground = Brushes.DarkGreen;
            }
            else
            {
                StoreCheckInt.Foreground = Brushes.DarkRed;
            }
        }

        private bool IsTextAllowed(string sender)
        {
            Regex regex = new Regex(@"^\d+$"); //regex that matches disallowed text
            if (regex.IsMatch(sender))
            {
                return true;
            }
            if (!regex.IsMatch(sender))
            {
                return false;
            }
            else
            {
                throw new NotImplementedException("But how?");
            }
        }