private void BtnEdit_Click(object sender, RoutedEventArgs e)
        {
            User selectedUser = DGUser.SelectedItem as User;

            if (SelectedUser(selectedUser))
            {
                User           oldUser = selectedUser.Clone() as User;
                UserEditWindow uew     = new UserEditWindow(selectedUser, UserEditWindow.Option.EDIT);
                if (uew.ShowDialog() != true)
                {
                    int index = IndexOfSelectedUser(selectedUser.Username);
                    Data.Instance.Users[index] = oldUser;
                }
                else
                {
                    selectedUser.ChangeUsers();
                }
            }
        }
        private void BtnAdd_Click(object sender, RoutedEventArgs e)
        {
            UserEditWindow uew = new UserEditWindow(new User(), UserEditWindow.Option.ADDING);

            uew.ShowDialog();
        }