RSVP’d user can “check-in” to event if within 30 meters of venue and after event startTime

[neilsarkar]

This means we also need to ask for location permissions (and later, deal with the case where they are denied).

Also I'm assuming we're not doing background location, right? Bc battery drain? So we might need to do geofencing in order to detect that they're near the venue while the app is closed.