Change Common so that the common cartridge import is handled by Lessons CC import code. The Commons code currently handles only an older version of the CC spec, and doesn't implement key parts of that spec.
The Lessons code isn't organized to allow selection of individual items, so for the moment this will show the cartridge as a single item to be imported.
Note that the import code will typically add lessons to the site, but it won't add other tools such as Assignment or Samigo. If the cartridge has items that require one of those tools and the tool isn't there, the attempt to import the item will fail. This seems to be consistent with the behavior of Blackboard import.