Updated PropTypes

[timdorr]

Depending on how #3205 shakes out, this provides updated and correct PropTypes.

[taion]

Let's change this up a bit.

I don't think exporting PropTypes as-is from the index is useful. It makes it a bit tricky to actually use the prop types in a straightforward way that avoids naming collisions.

Additionally, many of these prop types don't make sense to export:

• history is deprecated as a public API point
• location belongs to the history library
• component and components are never exposed to users
• route and routes are set up for internal use rather than external use (e.g. route will never be an element as supplied to a route component)
• Nobody should be importing falsy as a prop type from React Router

We should do the following:

• For now, keep exporting PropTypes to avoid breaking the API
• Going forward, only export the router prop type, and export it at top level as routerShape

That way, I can write my code as:

import { routerShape } from 'react-router';

export default class MyComponent extends React.Component {
  static contextTypes = {
    router: routerShape.isRequired,
  };

  /* ... */
}