Clean up exported PropTypes

[taion]

Closes #3205, #3342

This does a few things:

• Rename the exported location and router prop types to locationShape and routerShape, and export them at top-level from react-router
• Deprecate all the old internal prop types that should not have been exported
• Deprecate the old location and router prop type names
• Add back the removed prop types per Exported PropTypes object only includes { history, location, router }, breaking semver #3342

[taion]

I changed back the v2.0.0 upgrade guide because these prop types (nor router) were not available on v2.0.0.

I otherwise updated the docs and examples to use routerShape as appropriate.

[timdorr]

LGTM