Fix React propTypes deprecation from a library

[stevegrossi]

Then remove this from test_helper:

Application.put_env(:wallaby, :js_errors, false)

[stevegrossi]

This will seemingly involve updating react-router (where some of the propTypes warnings are coming from) from 3.x to 4.x, which made some fundamental changes. Some tips for upgrading:

• https://codeburst.io/react-router-v4-unofficial-migration-guide-5a370b8905a
• https://github.com/ReactTraining/react-router/blob/master/packages/react-router/docs/guides/migrating.md