Switch to using Pipenv in containers

[NiallEgan]

Task Description

As discussed in technical chapter, we should probably switch to using pipenv in containers instead of requirements.txt because:

• Gives us greater determinacy in our builds
• Stops duplication of requirements in the setup.py and requirements.txt
• Makes it easier to identify security vulnerabilities because we have an explicit list of versioned dependencies

Acceptance Criteria

• Our containers should use Pipfile and Pipfile.lock to install dependencies

Analytics Requirements