Retrospective approval of 2D pipeline-related changes

The implementation of the 2D pipeline (most notably in PIPE2D-310) involved several changes to the datamodel that were not approved through the usual change control procedure, but were nevertheless merged. This ticket seeks retrospective approval for those changes.

I will survey the 2D pipeline products as currently implemented, use this to update datamodel.txt, and provide a summary here of the changes which can be debated.