Add announcements (#12662)

* 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

app/javascript/mastodon/features/home_timeline/index.js

@@ -9,6 +9,7 @@ import { addColumn, removeColumn, moveColumn } from '../../actions/columns';
 import { defineMessages, injectIntl, FormattedMessage } from 'react-intl';
 import ColumnSettingsContainer from './containers/column_settings_container';
 import { Link } from 'react-router-dom';
+import AnnouncementsContainer from 'mastodon/features/getting_started/containers/announcements_container';
 
 const messages = defineMessages({
   title: { id: 'column.home', defaultMessage: 'Home' },
@@ -113,6 +114,8 @@ class HomeTimeline extends React.PureComponent {
         </ColumnHeader>
 
         <StatusListContainer
+          prepend={<AnnouncementsContainer />}
+          alwaysPrepend
           trackScroll={!pinned}
           scrollKey={`home_timeline-${columnId}`}
           onLoadMore={this.handleLoadMore}