In preparation for introducing batched e-mails, this splits up each of our e-mail templates into containers (which just have headers like the auto-generated email blob and footers like signatures) and content. There's a tiny bit of clean-up done but no actual changes have been made to the content of the emails themselves. Testing Done: Looked at email preview views for review requests, reviews, and review replies in both html and text formats. Saw everything work as expected.