The Captions enactor should work for videos added dynamically after page load

Currently the Captions preference can set the captions of embedded YouTube videos. However, if the video is dynamically added after page load, the enactor will not be able to locate the video to setup the necessary bindings. The enactor should be improved to listen for new iframes added and setup the necessary bindings if new video elements are found.

Look into Mutation Observer ( https://developer.mozilla.org/en-US/docs/Web/API/MutationObserver )