Upgrade `babel-loader` and remove the cache directory configuration
that was added in #620. `babel-loader` now uses the
`./node_modules/.cache/babel-loader` directory by default, so the
custom config is no longer needed.
* Move ESLint configuration to a separate package
* Remove the ESLint configuration, moved to eslint-config-react-app
* Update ESLint instructions
* Pin the package versions in eslint-config-react-app
* Add a README for eslint-config-react-app
* Update README.md
* Update README.md
* Update README.md
* Update README.md
* Update package.json
* Update package.json
* Update production eslint-loader config
* Add the ESLint config to devDependencies of the repo