setup an express server

[alicewriteswrongs]

starting the work to set up an express server to serve up the maps!

then we can point something like maps.bostondisplacement.org at the little app.

edit: this will close #88

[alicewriteswrongs]

following some docs here: https://github.com/reactjs/react-router/blob/v1.0.0/docs/guides/basics/Histories.md#configuring-your-server

[alicewriteswrongs]

small breaking change, for heroku we want to have npm start start the production server. previously we had npm start initialize the hot-reload webpack dev server. that's been moved to dev-start, which means to start the development server you do npm run-script dev-start.

also previously we had build setup to do the webpack build for production, this has been changed to postinstall (which means that npm will automatically trigger a build of the application after the install finishes).

[alicewriteswrongs]

ok, this is coming along. things seem to be working ok.

the big lift that's left to do is replicating the navigation menu from the jekyll app...