* adds `?hash` to JS and CSS bundle URLs against caching in production
* uses `html-webpack-plugin` to generate html dynamically
* html based on template in `app/html/index.html`
* per-app html files no longer needed
* `build/` dir is now completely deleteable, and fully gitignored
* top-level `make` now requires `client/app` to pick up on html and
style changes
* cleaned up `server.js` code for production bundle testing
* added readme entry about testing production bundles
* get rid of gulp
* use webpack-dev-server to serve app.js
* express serves static files
* 2 webpack configs: local and production
* for development with backend, websocket URL is injected
* remove unneeded static files
