Support backing up CSV import files

[oubiwann]

Whenever logins/creds are imported the files are currently left as-is, and left for the user to delete. But in the event that -- in the course of importing/exporting -- something goes wrong in the browser, or the wrong files override creds in the wrong browser, it would great to have a history (encrypted).

• Add a backup db option
• Establish a format for storing browser cred export files (type, timestamp, file bytes, id)
• When importing, support the option of backing up and encrypting the entire file
• When backing up the file, support the option of deleting the source file (only after checksum pass, and successful storage ... and maybe retrieval check too)
• Allow listing of all imports
• Allow writing one backed up bytes back to a file
• Allow writing all backup up bytes to files