updated endpoint for rizzo nav to hit Luna

Please review. Dependent on https://github.com/lonelyplanet/luna/pull/289

KNOWN ISSUE: Luna has no awareness of messages, so is unable to send an unread message count. I'm open to idea of how to retrieve that count.
This function was moved to [user_feed.js](https://github.com/lonelyplanet/rizzo/blob/online-status/app/assets/javascripts/lib/core/user_feed.js#L76-L81), as @robuye requested.