"Staging" covers the meaning of what is actually happening better than
"deploy". I want to keep "deploy" for actually deploying onto a production
server.
- Ubuntu 17.10 → 18.04.
- Python 3.6.3 → 3.6.6.
- Use `DEBIAN_FRONTEND=noninteractive` to prevent prompts during
installation.
- Install `tzdata` in the base image as it's required by subimages.
- Correctly set maintainer in Dockerfile.
