Internalize dependency on "jupyter-jvm-basekernel"

[andrus]

JJava (same as its ancestor, iJava) depends on io.github.spencerpark:jupyter-jvm-basekernel that is no longer supported. Among other things, this causes dependency issues like #31.

We will need to internalize io.github.spencerpark:jupyter-jvm-basekernel, either as a separate subproject of DFLib, but more likely as a module in a multi-module jjava project. Then we can fully control the dependency stack, etc. E.g. we can start by upgrading gson dependency, and then switch to something else (or shade the dependency).

[andrus]

@stariy95 , interestingly, even though we override the GSON dependency to 2.8.9 in JJava, the user still sees 2.8.5 per #31 🤔