- move every docker build material in a per-container dedicated directory
- use entrypoint.sh files as entrypoints
- simplify a lot the Dockerfile: we only pip install what's necessary, the
possibility of using swh packages from sources is done by detecting and
installing every repo found in /src/swh-*. It's the responsibility of the
user to mount local source directories via docker volumes.
- rewrite the docker-compose file accordingly, using env vars when needed.