First, rough attempt at internationalization of emails.
Throw a proper error if i18n-abide doesn't work as we expect.
Fix pass-through of preVerified flag in account creation.
Don't put unused 'account' value in the handlebars template context.
Rename request.preferredLang => request.app.preferredLang
Merge pull request #365 from mozilla/email-i18n

Internationalisation of emails