Creating the ATAT database requires a separate connection to one of the
default Postgres databases, like `postgres`. This updates the scripts
and secrets-tool command to handle creating the database. It also
removes database creation from Terraform and updates the documentation.
Dockerfile is now a single multi-stage build that relies on a Python 3.7
base image.
Notes:
- This builds uWSGI with a `pip install` because the Alpine vendored
uWSGI is built against Python 3.6.
- Adds a docker-compose file that can be used for testing that the build
works. It is not usable for development purposes because it creates a
static copy of the application.
