Full python launcher. Introducing STUN.

This is a proper rebase of `gubatron:openbazaar-python-launcher2`, which is not exactly the same as #780. Some refactorings and fixes have been squashed. Please review and test.
I think there's a PR that sets `LOG_LEVEL=30` on `run.sh` which is now gone. Let's not forget to do that here, either now, or after it gets merged.