Single Dockerfile for building ATAT.

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.

.dockerignore

@@ -1,9 +1,11 @@
-# Files to exclude from COPY and ADD commands when 
+# Files to exclude from COPY and ADD commands when
 # building a docker image from this directory
 
 # Exclude Docker build related files
 Dockerfile
+Dockerfile.nginx
 .dockerignore
+docker-compose.yml
 
 # Exclude the git directory and gitignore file
 .git
@@ -27,3 +29,7 @@ requirements.yml
 
 # Skip kubernetes and Docker config stuff
 deploy
+
+# exclude build artifacts and docker directories
+.venv
+node_modules