Support Data Resource mimetype directly in classic

[rgbkrk]

mimetype: application/vnd.dataresource+json

Similar to #2683, support the data resource mimetype out of the box just like jupyterlab and the nteract frontends.

Pandas is one of the libraries supporting this mimetype: pandas-dev/pandas#14904

/cc @gnestor

[takluyver]

This will be bumped again soon unless someone wants to tackle it.

[rgbkrk]

This is wholly dependent on getting the React PR in, which depends on the testing changes you're working on. I think we're safe to say we'll keep bumping this one until much later.

[takluyver]

Thanks - I've moved it to backlog so we can stop bumping it for every release.

[rgbkrk]

Cool, thanks.