[WIP] Migrate HtmlVversion to HTML attachments

Unfortunately this isn't finished, but I'm about to go away on holiday and won't be available to carry on with it when I come back. I'm afraid I'm going to have to hand it over to somebody else. You can see a detailed list of what I've done, and what's still to do on the story.

https://www.pivotaltracker.com/story/show/53797983

Feel free to email me questions if any of those tasks don't make sense (or ask me to drop into Campfire, etc). Just be aware that I currently expect to have fairly poor net access between 27 September and 5 October...