Facebook account creation not working

[patcon]

Re-ticketed from Gitter: https://gitter.im/pol-is/polisDeployment?at=5f2ede7379da21426f20cf51

@sarilouis wrote about an issue on the production website at pol.is:

when I try to login with Facebook, I get an error that the application is misconfigured I think it's got something to do with the Polis app settings in Facebook.

[patcon]

Going to mark this as high-priority, as it came out in sync-up convo that this is critical to polis' use in Lebanon's crisis: https://hackmd.io/@patcon/B19Vz-kzw

cc: @patrickas