Merge branch 'formatting_emails_75347616' into html_emails

Conflicts:
	app/views/prison_mailer/booking_request_email.html.haml
Fix HTML email previews
Update copy for rich text format (HTML)
Show missing reference numbers on visit mailer previews
Update HTML emails with banned and non-listed visitor content
General mark-up fixes to HTML emails
Partial fixes for HTML email specs.
Update visitor mailer specs for banned/unlisted
Convert all email styles to inline
Fix request email for single slot selections
Hard-code GOVUK image URL for mailers
Merge pull request #109 from ministryofjustice/html_emails

HTML emails