Client contact!

• When a backup is triggered through any means, all connected operators that have the mod will receive a toast showing the backup progress.
• This is just text on 1.7.10.
• Currently, there aren't any configs for this. There will be some in future.

Reduce minimum value for mintimer config to 0.25 / 15 minutes

Check file hashes rather than modification dates when making a differential / incremental backup

• Fixes #33
• This does make backups slower, especially on larger worlds, but is worth the extra slowdown.

New config option for whether to flush, which was previously supported (then removed due to lag) behaviour.

• This is usually never needed because of the above change.