Backup manager and engine databases

We need to add a backup system for local databases.

The final implementation does the following:

• It runs every hour, as well as on exit before trying to stop threads (a potential cause of database corruption).
• It dumps the database into a "backups" folder, and appends a timestamp to the original filename.
• It deletes backups older than 24 hours upon saving a new one.
• In case of database error on startup, it restores the most recent backup.