Mark backup as important

Important backups wouldn’t be overwritten—you could simply mark them so they’re protected. That would be useful if you manually save a really good state from time to time, for example on a Minecraft server where you know nothing has been griefed. If you’re away for a few weeks and something worse happens, in the worst case all the backups could be overwritten. Something like this would be pretty nice. I know there’s rsync and so on; I just thought it would be nice to have in zapx.