Added FileWrangler. Rewired wranglers.

Wrangler class hierarchy is now this:

    Wrangler
        FileWrangler
            BuildFileWrangler
            DistributionFileWrangler
            MakerModuleWrangler
            StylesheetWrangler
        PackageWrangler
            MaterialManagerWrangler
            MaterialPackageWrangler
            ScorePackageWrangler
            SegmentPackageWrangler