fixes https://github.com/TryGhost/Team/issues/2705
- Added showPostTitleSection to newsletter model in admin
- Wired up UI to admin model so it saves to the database
- Implemented showPostTitleSection in newsletter preview and added some
minor temporary css styling
- Implemented showPostTitleSection in newsletter template in backend,
and added some extra CSS styling to fix spacing
fixes https://github.com/TryGhost/Team/issues/2308
- Still has some missing pieces, but mostly works.
- Uses new handlebars template for emails
- When sending emails with the new email stability flag enabled, one
test email is now sent via the default smtp ghost mailer.