Add new field for stats announcement state

This is required so that "cancelled" announcements can be queried
and listed separately on the front-end.
Merge pull request #281 from alphagov/add-stats-announcements-state

Add new field for stats announcement state
Add manual to manual_section schema

We want this for scoping search results to sections of a manual.
Merge pull request #282 from alphagov/add-manual-to-manual-section-schema

Add manual to manual_section schema