code: protected SigninPanel<T> newSigninPanel(final String id, final IModel<T> model)
  	{
  		return new SigninPanel<>(id, model);
  	}
docs: Factory method for creating the SigninPanel that contains the TextField for the email and
  password. This method is invoked in the constructor from the derived classes and can be
  overridden so users can provide their own version of a Component that contains the TextField
  for the email and password.
  
  @param id
  the id
  @param model
  the model
  @return the Component