It would be awesome if maps could expire

[rachellawson]

There are a number of situations where the content of a map can only be relied upon for a fixed length of time and a user of that map should be prompted to update it.

For example, if there was a TET map in .obf format, we could ensure that it was downloaded reasonably close to someone making a trip and ensure that as few people as possible would accidentally wander off on illegal trails, annoying the locals.

Maybe if the .obf format included an expiry date, we could start with prompting the user to update a set number of days before expiry?