Fix for issue #353

Backup format has changed slightly. One can import old backups, but due to their lack of the NULL information e.g. all NULL dates will be restored as 0000-00-00 (same as w/o the patch). One has to manually empty the "Valid until date" field on the Settings tab. Otherwise "Status" change will not work as expected, and maybe some other problems if a functionality relies on NULL values.

Also some file permissions are corrected (useless executable bits).