Include change note in govdelivery email body

The layout was suggested by Mark

https://www.pivotaltracker.com/story/show/47628197
Merge pull request #430 from alphagov/change-note-in-govuk-delivery-email-body

Include change note in govdelivery email body

https://www.pivotaltracker.com/story/show/47628197
Format dates in emails correctly

https://www.pivotaltracker.com/story/show/47816085