====== Draft ======
The backup module should provide a simple central API for a backup or restoring data from other modules. Not all data from all modules should be saved as backup, so let each module decide what to backup and what not. E.g. cached data should rather be cleaned than saved in a backup.

To end successfully, the backup *must* be validated after finishing. Every time. Mandatory. Can't stress this enough. The success status must be fed back to the user.

===== Implemented hooks of other modules =====
  * An icon should be shown in the status line that indicates whether the last backup was successful or not.
  * At application start: information about problems, if last update (during the night?) was (un)successful

===== Interfaces provided by this module =====
  * Data backup interface. Other modules can use this hook to uncomplicatedly save data into a backup. The customers of this hook must not know where the backup is saved (locally, Amazon S3, Dropbox, etc; if it is encrypted or not; etc.)