Find solution to preview changesets that are to be closed in the delta API

Created by: eseliger

Ideally, those would have either a changeset spec that says "close me", or no changeset spec which would indicate "i need to be closed". I think we would even want to keep those closed changesets in the campaign. It's good to track a little more than be missing some impact the campaign had, IMO. The latter idea would require that we either keep a changeset spec for tracked changesets, or that we can make a distinction like

if isNotTracked && current_spec == 0 { close() }
else {
 // ??? what do do then
}