Facebook auth support.

So far as I can tell, there's no way to force segment.io to turn analytics calls into dummy calls, or turn on a special mode for unit testing...  We have a development key, but we use that to test on stage/dev/etc, and I imagine we wouldn't want to include it in our unit tests and thus muddy that stage data.

Thus: unfortunately, I don't think there's a good way to unit test this, and acceptance tests also become tricky (we'd need to set the development key and get some automated way of fetching results from segment.io, but that sounds (a) potentially flakey and (b) leads to the same muddy-data issue).  Perhaps this just needs to be added to the manual test plan...?  Suggestions welcome.