toree with spark 3

This isn't exactly a bug, but a report.

I'm trying to get toree to work with spark 3. I've gotten 0.5.0 rc2 working, but it wasn't easy.

First, there's no pip version so I had to hack up a jupyter kernel directory.

I found that it would only work with Java 11. But with java 11, I needed

"JDK_JAVA_OPTIONS": "-Dscala.usejavacp=true",

I guess that's OK, but I think you can set that in the code.