Remove imports/init/renders from lets-plot descriptors (move to Integ…

[AndreiKingsley]

Remove init/imports/renders part from Lets-Plot descriptors. They've been moved to Integration in Lets-Plot Kotlin.

A Lets-Plot Kotlin release with these changes is required before we can merge!

[ileasile]

@AndreiKingsley I would suggest to create a separate module (artifact) for Jupyter support that will depend on others. It will help in three ways:

1. It will be possible to build it for JVM target 11 without changing the jvm version for the whole project that will allow render<*>() from the API
2. It will reduce a number of dependencies in descriptors to only one
3. It will reduce the current versions hassle

I can help if needed

[AndreiKingsley]

@ileasile let's discuss it here.