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.
@Ianfeather, @remybach I've turned poll into 2 scenarios which I don't know why I didn't do in the first place O_o (still learning).
Depending on screen width (look above) user will have user feed component hidden or visible. It's very simple - don't poll if component's hidden - check unread messages only to update responsive menu indicator (this is done once, on pageload/refresh).