Data export and data import

Currently, in the KSS only data export functions exist. Specifically, in the Managing Backups menu item there is also export and it is possible to restore the full backup and import it.

The data imports were included in the first versions, but it did not work with sufficient safety, so we removed the import functions. In the future, we plan to put in the data import functions, and in this framework the solution of the exports and imports of categories and entries as well.