* 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

* Change image URL in mailer to full path

* Add application_mailer.view_profile localization.

* HTML e-mails for NotificationMailer (except digest)

* Add HTML template for digest

* Fix build

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