Port of ambitious-arcgis-app-2018

This release is a direct React port of https://github.com/mjuniper/ambitious-arcgis-app-2018/, see that repository for more information on the motivation behind this application.

One difference in how the React application behaves is that when a previous session is restored from a cookie, the user information is not fetched until after the application renders (in the App's componentDidMount()). Otherwise I tried to make this as close to a 1:1 comparison to the Ember app.