Produce build that's refactored into separate front-end and backend

[IanMayo]

The app is currently a single Java desktop app.

I'd like experiment with Web UIs, and refactor it as follows:

• re-package models folders into Java service behind REST interface.
• re-package front-end and controllers into TypeScript/React. Thin model wrappers will be created, which delegate actual processing to the backend, via REST calls
• retain the Leaflet map, using it directly
• keep the UI layout/arrangement as it is now

Package up the application so that the front-end and backend are started together, running on the same server, with REST comms (including backend heartbeat)