Reintroduced PackageWrangler. MODEL.

MODEL: MaterialPackageWrangler, SegmentPackageWrangler, ScorePackageWrangler
all inherit from PackageWrangler. There's a considerable number of public
methods shared between these three concrete classes; PackageWrangler reduces
a fair amount of code duplication. PackageWrangler will also keep code compact
as the last of the mapped * commands are implemented. (Because it is exactly
the three package wranglers that afford mapped * commands.)

TESTS: Score Manager test battery now implements 900 tests.