Add Detox

[rmccue]

Adds Detox to run E2E tests. Requires a bit of setup, but works pretty well afterwards.

As a plus, we can use it to generate screenshots for the App Store :D

[rmccue]

Also, I haven't adjusted ESLint to add the Jest globals for Detox yet, so linting will fail for now.

[rmccue]

For some reason, --generate-screenshots manual isn't working for me. Once it does, we can finagle the generate-screenshots bit some more and pass an artifact directory manually to have a screenshots dir instead.