private void btnSave_Click(object sender, RoutedEventArgs e)
        {
            UserModel userModel = new UserModel(tbxFirstName.Text, tbxLastName.Text,
                                                tbxPasswordFirst.Password, tbxEmail.Text, tbxTele.Text);

            if (AddUser.ValidateAddUser(tbxFirstName, tbxLastName,
                                        tbxPasswordFirst, tbxPasswordSecond, tbxEmail, tbxTele))
            {
                if (cbxBoss.IsChecked == true)
                {
                    AddUser.AddBoss(userModel);
                    AddUser.ClearText(tbxFirstName, tbxLastName,
                                      tbxPasswordFirst, tbxPasswordSecond, tbxEmail, tbxTele, cbxBoss);
                    cbUser.Items.Clear();
                    HandleItems.FillUserList(cbUser);
                }
                else
                {
                    AddUser.AddNewUser(userModel);
                    AddUser.ClearText(tbxFirstName, tbxLastName,
                                      tbxPasswordFirst, tbxPasswordSecond, tbxEmail, tbxTele, cbxBoss);
                    cbUser.Items.Clear();
                    HandleItems.FillUserList(cbUser);
                }
            }
        }