Arcadia model REST service

Usage: arcadia-server [--bind IP:PORT] [--data-dir PATH] [--token-file PATH]

Defaults: 127.0.0.1:8787; platform-local ArcadiaStudio/server directory.
Token required for non-loopback binds. ARCADIA_SERVER_TOKEN is an alternative.
Keep the data directory on local storage. See docs/server.md for deployment and API limits.