WIP - Bug 742951 - changing email address

NOT READY TO MERGE, BUT READY TO START REVIEWING

I still need to verify that the new code for sending a triggered message with additional fields will work. Jess is going to set up a test triggered message in ET for me to play with.

But there are a lot of changes here, and I wanted to get this posted so reviewing could start.

I'll make any updates in separate commits and won't squash until we're ready to merge.