Add #state and cancel info to stats announcements

A StatisticsAnnouncement can now be in three states: "provisional";
"confirmed"; or "cancelled". This adds a new "state" method to the model
and makes sure this is propagated to the front-end models via Rummager
and StatisticsAnnouncementProvider. It also adds the "cancellation_date"
and "cancellation_reason" details to the front-end models.
adjust how state is displayed on front-end

As-per Guy's designs, we no longer include "(confirmed)" on confirmed
announcements and mark cancelled announcements as such on the main
stats announcements index page.
Show cancellation status on announcement page

Small issue with the alignment of the meta data for cancelled
announcements to deal with.
Correct typos
Styling tweaks for cancelling