Fix flakey cucumber steps

These steps occasionally time out trying to load the preview page. I
haven't been able to figure out why, but they seem to be alot more
reliable when we explicitly visit the preview path rather than using
the `visit_link_href` helper.
Move confirm_unpublish to workflow controller

This is closer to the action it relates to. Also makes it easier to
re-render the unpublish form when there is an error.
Unpublish failures re-renders unpublish form
Update guidance page to show archive information
Prepend "[Archived]" to archived docs page title

I'm using a helper because not every edition show action wraps the
edition in a presenter. Besides, not all edition types have a
presenter.
EditionUnpublisher builds unpublishing reason

Instead of having the controller build the Unpublishing on the edition
we pass in the details to the service object and let it get everything
to the correct state
Require explanation when archiving
Use document format name to describe document

header_title is set to "Operations in #{location}" for fatality
notices.