Simplify logic for updating server with FCM token, and do it more often

[adamwolf]

Let's poke the server every time the app is started, and every 7 days. (Every 7 days is in the best practices guide for FCM).

There's a bunch of logic in there now for caching the FCM token and deciding when to submit to the backend and when to remove from the backend--nope! Let's just poke the backend with the current token. The backend will drop ones more than 30 days old (that's what the FCM best practices guide says, anyway).

Cognata

• https://github.com/beeminder/beeminder/issues/4895
• https://github.com/beeminder/beeminder/commit/15acbd7e3e29b9f7d18ab507453217c43f26506e (commit that turned it on for everyone)
• https://github.com/beeminder/beeminder/pull/4901 (the beeta feature)

Verbata: google push notifications,

[adamwolf]

I put some time into this today. I have the code updated and removed, but it needs a little more testing before I'm OK saying this is done. (ready to put into a beta release, that is)

[adamwolf]

Deployed in 5.2.0

[dreeves]

Adam on what exactly the UVI is: "Changed when and how we give our servers the notification ID, fixing issues where the ID changed and we didn't give the new one to our servers"