Allow to set the 'AdditionalInformation' property from KFileItemDelegate for each...

Allow to set the 'AdditionalInformation' property from KFileItemDelegate for each folder. Use case:
- Icons view for images: set 'Size' as additional property
- Icons view for media: show 'MIME type' as additional property
- Default Icons view: don't show any addtional property for a clean layout.

TODO: KFileItemDelagate::AdditionalInformation intersects with KDirModel::Columns when used in combination with the details view. Assure that the user does not get confronted with such implementation details in the user interface.

svn path=/trunk/KDE/kdebase/apps/; revision=641525