Switch to webpack workflow

A set of changes to match Blip and Clamshell's front-end workflow with Webpack.

@cheddar Do you want to take a look and tell me what you think? Thanks!
Ok how about this?

- `npm start` will run by default in "development mode", i.e. it will rebuild the client app on the fly. I suggest this, because that is something that will always "work" (although not optimized for production).
- `SERVE_STATIC=true npm start` will expect the client to be fully built in the `dist/` directory, and serve the static files from there

Sounds fair? :)