- if no Openseadragon instance, use a VideoViewerReference (based on
  OSDReferences) to get canvas size & DOM element
- add 2 number fields to specify annotation start/end
- speed up build by removing umd (not used in our dev setup) and demo build
- remove conflicting dependencies
  Both removed dependencies are installed at a lower version by another
  dependence (immutable is installed by draft-js-*)