Import records from multiple FZC database backups

[JoselleAstrid]

We have some database backups which are snapshots of the ladder data over the years. The earliest one we still have is only from 2012, but backups have been taken more steadily in recent years, and for most of 2022 (as I write this in 2023) I'd been taking backups twice a month. We should use these imports to start building up PB histories for players.

Have the main data-import command take multiple DB backup files, reading in order either from earliest to latest, or latest to earliest. When someone's record for a particular chart changes, enter that as a new record into the new database. If the machine, splits, comments, etc. get updated over time for the same record, in general we'll want to use the latest version.

There are likely some complications to deal with. For example, if there's an obvious typo, or a suspicious time that got removed by mods, then those may have to be listed as exceptions so they don't get imported. Or, maybe we'd choose to actually import them with a 'deleted' flag.

It'll be easiest to import as much ladder data as possible from the beginning, because mass data imports can get much messier in a live website. That's why I'm keen on doing this early on.