Next.js no longer uses `jsonPageRes`.
This PR removes it from `en-us` and `zh-cn` documentation (formatting picked up some changes on zh-cn readme).
Also updated the Flow type def for `getInitialProps`.
Resolves#6363
The `with-flow` sample has some obsolete definitions which are unused by the sample code. Removing the un-imported declarations is the easiest approach.
Changes:
* updated packages
* moved the content of `layout` to `_app.js` and created simple `Page` component
* replaced `import * as React` because it is not necessary to import everything
* moved `next.js.flow` to `flow-typed` as it is default directory for library definitions
* updated the gif