Updating how derived fields are calculated.
Updating how derived fields are calculated.

This follows changes to field_descriptions.json, and also
acknowledges that one process might have several derives.

guardian/swarmize,guardian/swarmize,FreeSchoolHackers/swarmize,guardian/swarmize,FreeSchoolHackers/swarmize,FreeSchoolHackers/swarmize,FreeSchoolHackers/swarmize