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

![screen shot 2014-07-26 at 3 20 34 pm](https://cloud.githubusercontent.com/assets/303226/3712459/844de60a-1515-11e4-9eb9-2df5b5d553a7.png)