Allow running multiple languages at the same time

[filmor]

Instead of writing a new "separate" kernel for each language, maybe we could mix them such that every cell could be executed in the language of choice. This is in fact not hugely difficult, essentially we just need to "spin up" the respective languages by starting their applications. Since objects are mostly "compatible" due to Erlang's simple type system, we can probably even use a common variable store for all of them.