Update to follow Best Practices

[bhearsum]

• Use Docker & Docker Compose for running a local dev environment, based on the python:3 image
• Use pip-compile-multi, and Pyup.io for dependency management
  • See https://github.com/mozilla-releng/releng-rfcs/blob/master/rfcs/0022-app-best-practices.md#dependency-management for requirements file details.
• Use tox as a test runner
• Use Taskcluster for CI
• Ensure production pushes happen manually, in response to bugs filed
• Ensure stage pushes happen in response to balrog_stage tags on Dockerhub
• Eliminate the development environment, if it exists

(Remove items that are not applicable to this project).