Add missing binaries in dockerfile (for gunicorn)

[spwoodcock]

I realised in e5a39f7 that I missed copying the locally installed binaries.

This means that gunicorn was not available in the path, and the container could not start up.

This PR:

• Adds the bins to the final image stage, making gunicorn command available.
• I also correctly added the python libs under site-packages, where they should be by default 👍