Explicitly pass iconNameForUrl when creating new places entry

Once KIO::iconNameForUrl returns special icons for standard paths (e.g. Video folder)
this will ensure when adding such a folder to places it will automatically get the proper icon.

Since KIO already depends on KBookmarks it can't depend the other way round, otherwise
this would have been fixed in KBookmarks directly.

Differential Revision: https://phabricator.kde.org/D3896