Reinstate FileWrangler.

The wrangler class hierarchy is now this:

    Wrangler
        FileWrangler
            BuildFileWrangler
            DistributionFileWrangler
            MakerFileWrangler
            StylesheetWrangler
        PackageWrangler
            ScorePackageWrangler
            ScoreInternalPackageWrangler
                MaterialPackageWrangler
                SegmentPackageWrangler