Wrote ScorePackageManager.write_stub_initializer() tests. MILESTONE.

MILESTONE: tests now exist for ALL manager public methods; tests also now exist
for ALL wrangler public methods.

MILESTONE: primary Score Manager testing is now complete.

More tests and changes to tests will continue to come in over the next couple
of days. But the work from here on is essentiallys all iterative revision.

It is possible for the first time to think about a first Score Manager release.