Allow Java VM restart

[dg46]

Currently, the Java VM cannot be restarted after it is shut down.
This limitation can be avoided if we run all tasks that require the VM in a separate process using the multiprocessing module: LeeKamentsky/python-javabridge#88
This would also allow us to run many causal discovery procedures in parallel. A downside is that the start of a new process adds additional overhead that will affect the runtime of an analysis.

[dg46]

The issue is fixed for Windows on a separate branch (fix-java-vm). Unfortunately, the differences in multiprocessing between Linux and Windows lead to failing tests in the CI pipeline for the Linux builds.
I cannot properly debug this at the moment, so for now the proposed solution is to clone the version from the fix-java-vm branch in case you need to restart the Java VM in any downstream tasks.