Don't prefix methods with "govuk_delivery"

Now this stuff is encapsulated in its own class, we don't need the
long unweildy method names
Add document type to gov delivery email titles

This also tweaks the way change notes are rendered as we no longer
prefix the title with "Updated"
Update Gov UK Delivery job to use correct title
Merge pull request #478 from alphagov/govdelivery-email-titles

Govdelivery email titles

https://www.pivotaltracker.com/story/show/48417837