Add some ENV vars for init

[nkottary]

• JAVACALL_IGNORE_WORKERS: If myid() is in this list then JVM is not initialized. This is useful when you don't want JVM to load on certain workers.
• JAVACALL_MEMORY_LIMIT: This is the heap size limit.

[aviks]

This is useful, but shouldn't these go into JavaCall.jl directly?

[nkottary]

Okay. I've opened this: https://github.com/JuliaInterop/JavaCall.jl/pull/97