Refactor with modular reporting

[Sean Morgan]

Today, we have one output format (ConsoleReport) which provides a stdout interface. As part of our refactor, we're going to make this selectable and add a JSONReport option with the ability to serialize results to disk.

Going forward, this will enable users to easily add their own output format if the built-in methods are not sufficient.

Tasks:

• Add constants for our available reporting modules and default reporting module
• Refactor Modelscan.scan to specify reporting module
• Add JSONReport functionality to the repo
• Refactor CLI for modularized reporting

[Sean Morgan]

Supersedes #40 and #38