Adds event after State address field swap is complete.

We are using the [Chosen jQuery plugin](http://harvesthq.github.io/chosen/) for select lists on all forms, including Recurly.js forms. We ran into an issue when the State address field on the Billing form is swapped between a text field and a select list depending on the value of the Country field. We needed to reapply Chosen each time the swap for a select list is made. We found that the easiest way to do that was to trigger an event after the swap is complete.