Fix initialization of Universe.CURRENT

- seemingly we need a main.py to make sure that Universe is loaded exactly once

Signed-off-by: Stefan Marr <git@stefan-marr.de>
Split message_node.py into different files

- this helps resolving include dependencies

Signed-off-by: Stefan Marr <git@stefan-marr.de>
Use a module-level global for current universe.

Signed-off-by: Stefan Marr <git@stefan-marr.de>