Implement "Restore" in setup.pl

[sbts]

We already have a backup option.
We need to add a restore option.

We already have a Sysconfig variable "backupdir" I'd say we should simply present a filtered list of files to restore from there.
Those files should be real files, not symlinks, and match a regex along the lines of
$DBname.*\.$backupExtension

That way there is no risk of file discovery on the server,

Of course this assumes the autonaming of generated backups matches that regex

The above mechanism removes the need to either allow Huge Uploads, or server Filesystem browsing

In the future we may want to allow copy paste of an scp or http URI with appropriate Auth prompts, although that's out of scope for this issue.