Add event listeners for transition events.

[brian-mcallister-lab49]

We could add the ability for users to subscribe to transition events in the UI, so that if you wanted to link together some callback and the state of the UI, you could accomplish that.

We'd likely need to listen to this event: https://developer.mozilla.org/en-US/docs/Web/API/HTMLElement/transitionend_event

As far as the API, I'm not entirely sure what the best option is. We may need to rely on React refs to accomplish this.