Change `all_day` to be a visual client-side cue only
Publish immediately if `scheduled_at` is in the past
Add `published_at` and `updated_at` to announcements JSON
* Move announcements above scroll container; add button to temporarily hide them
* Remove interface for dismissing announcements
* Display number of unread announcements
* Count unread announcements accurately
* Fix size of announcement box not fitting the currently displayed announcement
* Fix announcement box background color to match button color
* Add announcements
Fix#11006
* Add reactions to announcements
* Add admin UI for announcements
* Add unit tests
* Fix issues
- Add `with_dismissed` param to announcements API
- Fix end date not being formatted when time range is given
- Fix announcement delete causing reactions to send streaming updates
- Fix announcements container growing too wide and mascot too small
- Fix `all_day` being settable when no time range is given
- Change text "Update" to "Announcement"
* Fix scheduler unpublishing announcements before they are due
* Fix filter params not being passed to announcements filter
