Publish additional context to the Aphlict server.

Summary:
Ref T4324. As well as sending the key for the notification, also publish the notification type and a list of subscribers to the Aphlict server.

The idea here is that the Aphlict server passes anything within the `data` key to the clients, whereas other keys (such as `subscribers`) will be used by the server to determine where the notifications should be routed.

Note that these changes don't do anything useful, but are a prerequisite for further work on T4324.

Test Plan:
Sent myself test notifications at `/notification/status/`. Also inspected the Aphlict server debug output:

```
> sudo ./bin/aphlict --foreground
Starting server in foreground, ignoring pidfile...
Launching server:

    $ node '/usr/src/phabricator/support/aphlict/server/aphlict_server.js' --port='22280' --admin='22281' --host='localhost' --user='aphlict' --log='/var/log/aphlict.log'

[Thu Jun 05 2014 18:38:14 GMT+0000 (UTC)] Started Server (PID 15437)
[Thu Jun 05 2014 18:38:16 GMT+0000 (UTC)] <FlashPolicy> Policy Request From ::ffff:10.0.0.1
[Thu Jun 05 2014 18:38:16 GMT+0000 (UTC)] <Listener/1> Connected from ::ffff:10.0.0.1
[Thu Jun 05 2014 18:38:19 GMT+0000 (UTC)] notification: {"data":{"key":"6021516228036848559","type":"notification"},"subscribers":["PHID-USER-cb5af6p4oepy5tlgqypi"]}
[Thu Jun 05 2014 18:38:19 GMT+0000 (UTC)] <Listener/1> Wrote Message
```

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: epriestley, Korvin

Maniphest Tasks: T4324

Differential Revision: https://secure.phabricator.com/D9396