Syntax highlighting issue in JupyterLab 1.0

[krassowski]

Just giving you heads up that there are reports of IJulia kernel not communicating well with the recent JupyterLab in version 1.0 (see jupyterlab/jupyterlab#6760 and jupyterlab/jupyterlab#6826).

The cause is likely that the status field is now strictly checked in the response for "kernel_info_request", and notebooks with kernels which do not include it do not get that language specification (and thus syntax highlighting, among others) - at least this was the problem for R, which got recently fixed (IRkernel/IRkernel#636).

In response to this findings, the documentation for the status field in kernel messages was harmonized jupyter/jupyter_client#454 to clarify the specification.