Option to list all currently active backups

[cocoonkid]

it would be great to be able to just list all active/working backups.
I always have to manually lookup the backup files in the cloud and verify there.

[xplosionmind]

I totally second this! As of right now, mackup list lists all the supported apps, while I believe that running mackup list should only display applications that are currently being backed up.

Listing all of the supported apps should be triggered by the mackup list --all command, instead.

[joshmedeski]

PRs are welcome, you'll have to do some sort of lookup on the symlinks to detect if mackup is currently backing up an app.

A general, creating a reusable checkIfInUse function could help with other feature requests I've seen.