Support Comm messages in the Kernel API

[belovrv]

Support Comm messages in the Kernel API. They will help to make interactive dataframes in the Kernel

[altavir]

Currently we are doing dynamic message exchange by creating a separate ktor server. But it would be nice to be able to communicate directly via Jupyter connection.

I think it will require some kind of front-end part for Kotlin Jupyter API library to support it properly.

[ileasile]

Merged. Will try dev version with Datafame and maybe adjust or extend API then.