protected void Button1_Click(object sender, EventArgs e)
{
var targetUser = this.context.Users.Where(u => u.UserName == this.UsersDropdown.SelectedItem.Text).First();
targetUser.Roles.Clear();
this.context.SaveChanges();
Notifier.AddErrorMessage(string.Format("User {0}, banned for further bookings!", targetUser.UserName));
}