Add linting npm script

To make it easier to use eslint, wrap it in an npm script.

Command to lint all files: `node_modules/eslint/bin/eslint.js -c ../.eslintrc.json ./`

We can add this to the scripts in package.json. Extra points if we can figure out how to pass arguments through npm scripts to enable a file-specific interface instead of just the entire directory:

`npm run lint components/newcomponent/component.js`