Backups must be encrypted and versioned #16
Description
As the time passes the app will update, and its database structure may change, and with that older backups could be incompatible with the new structure when restored in the new version, because of that is needed that the backup is made versioned with a flag in it, and it should have a mechanism in the restore code that identifies the version of the backup when restoring from the file and from that making the needed changes in the data to shape that in the new data format. Also, the backup file cant have the data as plain json, it should be encrypted in a way that is reversible but no deciphable, it should be fast and light and totally offline.