Improvements

[davidsiaw]

Introducing some nice improvements:

Generate models with uuid for foreign keys, and generate timestamps correctly
Add concern helper to assist with writing concern specs
Show how to make constants in specs (if you don't need a factory)

[azusabot]

	2 Warnings
⚠️	We really appreciate pull requests that demonstrate issues, even without a fix. That said, the next step is to try and fix the failing tests!
⚠️	External contributor has edited these files: Gemfile

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