Improve minimum App version / force update handling

[lorenjohnson]

As of this release, and a couple in the past, earlier versions of the app will not run properly on the current API. We need a mechanism to sense when an older app is running and to force an update. Unfortunately it's too late for this release, but if we introduce it now it'll be there for us when we need it next... Which may not be long.

We implemented a minimal check and message before which I assumed was no longer working, but after reviewing it and setting the corresponding ENV VAR on hylo-node production. IT WORKS!

The current message will still allow you to use the app but will present you with a message that "this version is no longer supported" and gives you a link to the current version in the App Store (or Play Store--but haven't tested that yet).

All in all, it's good enough, and could use improvement. Like we should probably not let a user auth even if the app is out of date and we want to force and update, as there are cases where it could potentially be destructive, not just a bad UX, to have someone on the old API...

Will need minimal friendly UI for the case of needing to force an update.

Probably start with this: https://github.com/tessus/react-native-version-info / https://medium.com/@kinley.tshering/force-update-react-native-apps-a9c1f22c0701

^^ That would be much nicer as it would directly query the stores themselves for the current latest version and we could set it to automatically deprecate a version on a major version move (like a move from 4.x to 5.x).