Footnotes in the backmatter are given the footnote's number as a label.
The articleauthoring output is unaffected from this change, as footnotes
are placed inline there.
Closes: #7210
New formats:
- `jats_archiving` for the "Archiving and Interchange Tag Set",
- `jats_publishing` for the "Journal Publishing Tag Set", and
- `jats_articleauthoring` for the "Article Authoring Tag Set."
The "jats" output format is now an alias for "jats_archiving".
Closes: #6014
