Make Pager support AJAX

In #825692: Pager or navigation for the carousel, we added support for a Pager, but it didn't work with AJAX-enabled carousels. Adding AJAX support for the pager is actually surprisingly little work. The only missing piece is that JavaScript doesn't know how many total items there are in the carousel, but we've already calculated this value in the Views integration and passed it as a JavaScript setting. All we need to do is use this number in our pager support and everything works together.