Annotate CR publications with substantive status

[plehegar]

Some CR gets published without the Director's approval and, in theory, only contain editorial changes.

Some CRs gets published with the Director's approval and do contain substantive changes, thus becoming a reference draft for the Patent Policy.

It would be nice to differentiate them in the API so that, for a given CR version, it's possible to determine what was the latest reference draft used for it (could be FPWD or a previous CR).

For a CR that has a WD as a previous version, it is automatically substantive and used in IPP.

Something "substantive": "true",
or "reference-draft": "true" would do it.

Use cases:

• the Director diff tool needs to use the latest reference draft when looking at a new CR/PR publication (unless the previous version was a WD)
• the email announcer of public-review-announce should not send email on a new CR if it doesn't have substantive changes (unless the previous version was a WD)