put config in node version

- index.js now provides a config
- introduced the concept of screen, which will be associated with each
board layout, multiple users may use the same screen
- message event is now handled in one place
- board sends a message to the server (if one present) for configuration
- added a poll button to the board (to get server data)
- created a single _dependencies.ts file (because dependencies out of
order will silently break tsc)