In Devise::Mailer#email_changed, the new email might be in the email attr.
See: https://github.com/plataformatec/devise/blob/master/app/views/devise/mailer/email_changed.html.erb

* Use PNG images in HTML e-mails

* Make webpack use URLs with host so fonts load inside HTML e-mails

Convert this back to a relative URL in the premailer CSS loader
since local requests are quicker

* Improve responsive design

* Add missing PNG icon

- premailer gem to turn CSS into inline styles automatically
- rework UserMailer templates
- reword UserMailer templates