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/getting_started/containers/announcements_container.js

@@ -0,0 +1,21 @@
+import { connect } from 'react-redux';
+import { fetchAnnouncements, dismissAnnouncement, addReaction, removeReaction } from 'mastodon/actions/announcements';
+import Announcements from '../components/announcements';
+import { createSelector } from 'reselect';
+import { Map as ImmutableMap } from 'immutable';
+
+const customEmojiMap = createSelector([state => state.get('custom_emojis')], items => items.reduce((map, emoji) => map.set(emoji.get('shortcode'), emoji), ImmutableMap()));
+
+const mapStateToProps = state => ({
+  announcements: state.getIn(['announcements', 'items']),
+  emojiMap: customEmojiMap(state),
+});
+
+const mapDispatchToProps = dispatch => ({
+  fetchAnnouncements: () => dispatch(fetchAnnouncements()),
+  dismissAnnouncement: id => dispatch(dismissAnnouncement(id)),
+  addReaction: (id, name) => dispatch(addReaction(id, name)),
+  removeReaction: (id, name) => dispatch(removeReaction(id, name)),
+});
+
+export default connect(mapStateToProps, mapDispatchToProps)(Announcements);