Added ulSelector and liSelector into the options for selector customization

Added ulSelector and liSelector for the options to customize the corresponding jQuery DOM selectors.
@gnarf :+1: . This would definitely break the page nav. It would even break if `o.ulSelector` were a tagName other than `ol` or `ul` since the page nav items are created as `li`s. Also, I think it would make the proposed `ulSelector` option do more than expected, making it responsible not only for selecting the "ul" containing the carousel items themselves, but also for creating the page nav.