feat(developer): Keyman Developer Server

Initial commit for Keyman Developer Server, running on Node.

Supports web debugger only at this point.

Extensive rewrite of web debugger, much of it more modern standards,
significantly improved UX:

1. Drop keyboards, packages, fonts, models onto debug page to load them
2. Websocket for instant reload of recompiled keyboards, packages,
   models.
3. API for interacting with debug server.
4. Cache of recently used items.
5. Integration with ngrok for public access as desired.
6. Tray icon (currently default icon) for control of server.
7. Server can live after TIKE closes, supports multiple TIKE instances.
8. UI of debug host page rewritten with Bootstrap.
9. Packages downloads integrated into main page, and download link for
   Keyman supports all platforms (Linux is just a link to
   instructions...)
10. Avoids file locking and contention by managing all files internally.
11. Not yet tested, but should run cross-platform.