Added ability to prevent dialog from closing

[matiasjuliobello]

Changed onConfirm event to determine whether the dialog should close or not, depending upon if entry is accepted as valid.
For instance, something like this:

onConfirm: (values) 
{
	if (values.length > 3)
	{
	  // show warning message
	  return false;
	}

	return true;
}