Add `enable-annotation` attribute to managed iframes to opt-in to annotation tools
Add `enable-annotation` attribute to managed iframes to opt-in to annotation tools

More info:
https://github.com/hypothesis/client/pull/533

readium/readium-shared-js,NYPL-Simplified/readium-shared-js,NYPL-Simplified/readium-shared-js,NYPL/readium-shared-js,NYPL/readium-shared-js,readium/readium-shared-js