Allow re-export of manuscript with annotations

[adam3smith]

I think we want to focus on .docx here, because roundtrip writing would be a principal motivation, but having it work for both PDF and .docx would be great.

[qqmyers]

Looking into the mechanics of writing a revised original. While I do that, some questions re: How would this work w.r.t.

• where do the annotations come from? Will the front end have them?
• where does the updated file go? Does it replace the original in Dataverse? Do the updated annotations replace the ones stored in Dataverse? (I.e. will subsequent calls to GET the doc and annotations via the annorep backend return the updated doc and annotations rather than the original?

Or?