Merge pull request
#4533 from ivanov/display-isolated...
Merge pull request
#4533 from ivanov/display-isolated
propagate display metadata to all mimetypes
Additionally, this PR removes in-memory short keys in favor of using mimetype keys within the notebook javascript code, and tests toJSON/fromJSON codepaths for all of the supported mimetypes.
The change fixes the dropping of unrecognized mime-types from the notebook document.