Add eslint

[michelmansour]

This PR introduces eslint and the AirBnB ruleset for Javascript/React. Some other small changes are also included.

@drewrey All rules are open to discussion, now and in the future. I'd like to get your ok before merging.

[michelmansour]

Also, @drewrey, since there are so many changes, it would be great if you could check out this branch locally and test the app to make sure everything still works as expected.

[drewrey]

Running npm run lint, I get:

Cannot find module 'babel-eslint'

babel-eslint's install instructions use --save-dev, should we follow that? Do most people install javascript linters globally?

There's a note on babel-eslint's README suggesting we be able get by with just eslint (with some config) unless we use:

stuff like class properties, decorators, async/await, types.

I haven't noticed those things, but maybe they're already here, or maybe you intend to make use of them.

The app is working as expected for me. 👍

[michelmansour]

Running npm run lint, I get:

Cannot find module 'babel-eslint'

babel-eslint's install instructions use --save-dev, should we follow that? Do most people install javascript linters globally?

Oh, good catch. Forgot to include it in the dev-dependencies.

There's a note on babel-eslint's README suggesting we be able get by with just eslint (with some config) unless we use:

Yes, I noticed that, too, but it wasn't working for me without babel-eslint. I'll try again.

[michelmansour]

Actually, we are using class properties: defining instance methods using arrow function, so we do need babel-eslint. I'll add it to dev-dependencies.

[michelmansour]

Force pushed with babel-eslint included. Please try again.

[drewrey]

LGTM