Add statistics announcements link to admin menu
Restrict access to stats announcement feature

Only GDS editors and ONS users should be able to access the statistics
announcements stuff in admin for the time being so we can road test
the feature.
Don't show doc status on edit form

Document linking is now managed on the show page
tweak class names on linker links
Allow announcement linked documents to be changed

This allows a linked document to be changed after the fact so that
mistakes can be corrected.
Do not allow change notes on minor changes

If the change merely increases the precision of the release date, then
a change note is not required and should be rejected.
Toggle precision when release date is confirmed

If a release date is marked as confirmed, then we should fix the
precision to exact.
Rename javascript assets folder for consistency
Tie date changes to users
Add scenario for linking docs to announcements
Update step definitions to use new helper
Merge branch 'statistical-release-announcements' into announcable-statistics-frontend
Update feature to respect new stats announcement validation