linked session by fingerprint

Allow the linking of web and websocket connections via `connection.fingerprint`

- promote fingerprint to be a top-level connection element (`connection.fingerprint`)
  - previously `connection.rawConnection.fingerprint`
- add `connection.fingerprint` to websocket connections whenever possible via `api.config.servers.web.fingerprint.cookieKey`
- this is impossible to test without a real browser, so `/public/linkedSession.html` is provided to demonstrate