Add ability to export as *_toc.xml from "Review" page

*_toc.xml is the legacy format we use on IA. Being able to convert the tocky output JSON to this _toc.xml format would be useful for our partners.

Note for a first version, we can ignore the pixel regions present in _toc.xml

Sample toc xml: TODO

Start at the Review page and trace how tocky's output JSON is produced and exported. Review the legacy *_toc.xml format and obtain the missing sample before defining the conversion; pixel regions may be excluded in the first version. Done means the Review page can export valid *_toc.xml from the available JSON data.

Written by the indexing model from the issue text.