* Update eslint-plugin-react and enable new rules

New rules:
* `react/no-danger-with-children` (yannickcr/eslint-plugin-react#710)
* `react/no-find-dom-node` (yannickcr/eslint-plugin-react#678)
* `react/style-prop-object` (yannickcr/eslint-plugin-react#715)

* Remove react/no-find-dom-node for now

* 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

* Revert "Add ES5 version of `path-exists` to CLI"

This reverts commit fc3ab46d.

* Use pre node@4 compatible `path-exists`

Ref #617