for PyApp builds, remind the user if out-of-date

(Talking with Pete) we want to explore Mac, Windows etc builds via PyApp.

It would be nice if we could "remind" the user that they can run wormhole self update to get a new release.

We do not want any of the client builds "phoning home" and doing network activity without being asked. So there's a bit of a catch-22, where we'd like to learn about new builds (or tell the user "it has been a while, why not check").

Options:

• server could (once again) say something about what version(s) are current
  • used to do this ("recommended version") but now there are multiple client implementations
  • could public like "python": "0.23.0" to say what the current version is
  • pro: we're already contacting this server, so no additional network traffic
  • con: server operator(s) have to update something on ever client release
• local state (saved where?) could signal the client to bug the user to run wormhole self update
  • if "more than 6 months" AND "more than 30 days since last nag" THEN: nag user
  • where to save? ("place the OS puts user information" via libs etc)

Conclusion:

Do some form of the "local state" option, so:

• save local state for "last bugged user" in a file wherever platformdirs says
• if "this release's release date is more than 6 months ago" AND "we haven't recently bugged the user" THEN bug the user, and remember that we did that (in the above file)
• do not bug again until the "recently" amount of days have passed
• "recently" is 30 days
• edge cases:
  • if the platformdirs suggested directory fails for any reason (e.g. isn't writable) then we never bug the user