* 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

* Do not crash the whole UI when loading an invalid column

* Add error boundary component to catch Web UI crashes

* Add stack trace on supported browsers

* Add component stack info, pre-format everything for github

* Make “Reload” a clickable link that calls window.location.reload()

* Remove elephant friend from error boundary, make title stand out more

* Simplify error boundary to only a graphic