Save RSVP's

[samhill303]

I'd like to see if we can save our rsvp's to a user account so if you log in on a different device, you don't lose your settings.

I think the simplest solution would be to:

1. Add login with gmail to the Droidcon app
2. With that user info, push a list of session id's to firebase/firestore. We can alternatively do this on our backend server. To discuss.
3. Whatever place we keep the list, it should be a list and a "last update" timestamp. On app start, if logged in, check and see if that timestamp is newer than our last sync (we should keep last sync in internal settings). If newer, update our local values.
4. As the user is selecting sessions, we should push values to our central store (but also update the local last sync value so we don't overwrite our own changes).

It's a very basic sync algorithm. We can iterate on it a bit if needed. It's OK if we don't get perfection. This should be relatively rare.