Added extra attribute fields for additional styling.

While I'm sure this can be done more elegantly, I've added several new additional styling options. I've added the ability to set an id field for the navigation parent ul element. Also added ability to set a sub-ul (the inner page ul's) class. And finally an option to set a class on the li element instead of setting it directly on the link element.

Just figured maybe some of these extra styling options would be helpful to others too. Thanks.