Update dependencies

[lemonmade]

This PR updates all of our ESLint-related dependencies, including bumping ESLint to 3.x. It also adds a test to make sure that we configure every available rule, and adds some missing rules as a result of that. Here are some highlights:

• I reconfigured the "use stateless React components if you can" rule. I don't think there's a reason not to and it's a very good practice I'd like to encourage.
• Added a bunch of a11y-related ESLint rules
• Allowed constant conditions for loops, so you can do while (true) {}

Thoughts? @bouk @GoodForOneFare @Shopify/fed

[bouk]

can we delete our plugin now that this exists?

[lemonmade]

Good call. I think I am also going to turn off the required types for return/ parameter, generally I think inference is better and less overbearing. Let me know if you think that's a bad idea.