Multiple Sources and targets

[dnanian]

You can create settings for each source/target pair, and combine that with a copy script if you'd like: remember that a script is not volume specific -- it selects files from the files fed to you on a volume.

You can't combine multiple backups into a single schedule, but you can schedule > 1 for a given time, and we'll make them go back-to-back.

If a target is not mounted, we'll try to mount it if it's attached. Otherwise the backup will fail and move to the next run. We won't run "failed" backups: we'll just advance to the next scheduled time.