Facebook auth support.

- adds Facebook as a valid 3rd-party auth provider
- moves some moderately janky JS-based logging to the server-side
- maintains integrity of current login-based logging for both old and new 3rd-party-auth flows
Quick thoughts on this:
What's a "first-time" login? The first time "Bob" logs in, ever, or the first time some user logs in a given session / browser / etc? 

I'm inclined to think that this kind of data may be better evaluated reliably by querying the analytics output, where as "never_signed_in" may not be set in the session if multiple browsers are used, the user switches computers (starts on the tablet, gets tired and switched to a desktop) 

Anyway, just food for thought.