APAF's Secure Backup and Restore

[fpietrosanti]

This feature is to implement support for Backup and Restore APIs/functionalities of APAF's and APAF's applications.

Summary:
Every application running as a server, need to store customized configuration files, application settings, application data and so on.
However APAF's application will be probably server application in the hands of end-users, this means that the facilities normally required to manage the server should be usable also by an end-user.

Intro:
For the reason previously explained, apaf's made applications should support easy backup and restore functionality.

APAF should provide a way to let an APAF services to declare all it's data files, files customized and/or specific that require to be backed-up and restored, and to hook specific check and/or operations to be done during the backup/restore.

It's supposed that an APAF application's backup file, can be only restored on exactly the same version of the application.

The APAF support for backup and restore should handle all the integrity check verification of compliance between various backup/restore files.

From the end-user point of view the operations for backup and restore should be nothing more than downloading a backup file and uploading a backup file.

The backup file has to be secured, encrypted with a passphrase and/or PGP key of the node maintainer.

That's a topic to be discussed and evaluated cc @hellais @mmaker @sniffjoke @evilaliv3