In order to clean up vocabulary and better serve the needs of dynamic
pages, refactor `setupAnnotation` to deal with re-setup, unhighlighting
targets that have been removed from the annotation and re-anchoring
anchors that have lost their ranges.

- Store the Range on the anchor

  * The BucketBar would use it for getBoundingClientRect, except that
    it's a bit broken on Chrome.

  * The PDF Plugin can delete it to trigger re-anchoring no page load

- Use MutationObservers in the PDF plugin and make smarter judgements
  about when pages are done rendering by using the renderState in
  addition to the text layer renderingDone flag.