Fix bug in import viewer

Viewing an import containing documents that have been marked as
deleted was blowing up because of the lack of a `latest_edition`. This
allows deleted documents to be listed and marked as deleted
Remove unnecessary JavaScript jiggery-pokery

Instead of setting the value of the speed_save_convert parameter
using JavaScript, we turn the submit tag to a button with the value
set. It only gets posted if the button is clicked
Add speed-tagging date/times where appropriate.

The speed tagging view for various edition types get additional fields
to expose dates and times where appropriate.