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/styles/mastodon/components.scss

@@ -859,6 +859,44 @@
   }
 }
 
+.announcements__item__content {
+  word-wrap: break-word;
+
+  .emojione {
+    width: 20px;
+    height: 20px;
+    margin: -3px 0 0;
+  }
+
+  p {
+    margin-bottom: 10px;
+    white-space: pre-wrap;
+
+    &:last-child {
+      margin-bottom: 0;
+    }
+  }
+
+  a {
+    color: $highlight-text-color;
+    text-decoration: none;
+
+    &:hover {
+      text-decoration: underline;
+    }
+
+    &.mention {
+      &:hover {
+        text-decoration: none;
+
+        span {
+          text-decoration: underline;
+        }
+      }
+    }
+  }
+}
+
 .status__content.status__content--collapsed {
   max-height: 20px * 15; // 15 lines is roughly above 500 characters
 }
@@ -6581,3 +6619,178 @@ noscript {
     }
   }
 }
+
+.announcements {
+  background: lighten($ui-base-color, 4%);
+  border-top: 1px solid $ui-base-color;
+  font-size: 13px;
+  display: flex;
+  align-items: flex-end;
+
+  &__mastodon {
+    width: 124px;
+    flex: 0 0 auto;
+
+    @media screen and (max-width: 124px + 300px) {
+      display: none;
+    }
+  }
+
+  &__container {
+    width: calc(100% - 124px);
+    flex: 0 0 auto;
+    position: relative;
+
+    @media screen and (max-width: 124px + 300px) {
+      width: 100%;
+    }
+  }
+
+  &__item {
+    box-sizing: border-box;
+    width: 100%;
+    padding: 15px;
+    padding-right: 15px + 18px;
+    position: relative;
+
+    &__range {
+      display: block;
+      font-weight: 500;
+      margin-bottom: 10px;
+    }
+
+    &__dismiss-icon {
+      position: absolute;
+      top: 12px;
+      right: 12px;
+    }
+  }
+
+  &__pagination {
+    padding: 15px;
+    color: $darker-text-color;
+    position: absolute;
+    bottom: 3px;
+    right: 0;
+  }
+}
+
+.layout-multiple-columns .announcements__mastodon {
+  display: none;
+}
+
+.layout-multiple-columns .announcements__container {
+  width: 100%;
+}
+
+.reactions-bar {
+  display: flex;
+  flex-wrap: wrap;
+  align-items: center;
+  margin-top: 15px;
+  margin-left: -2px;
+  width: calc(100% - (90px - 33px));
+
+  &__item {
+    flex-shrink: 0;
+    background: lighten($ui-base-color, 12%);
+    border: 0;
+    border-radius: 3px;
+    margin: 2px;
+    cursor: pointer;
+    user-select: none;
+    padding: 0 6px;
+    display: flex;
+    align-items: center;
+    transition: all 100ms ease-in;
+    transition-property: background-color, color;
+
+    &__emoji {
+      display: block;
+      margin: 3px 0;
+      width: 16px;
+      height: 16px;
+
+      img {
+        display: block;
+        margin: 0;
+        width: 100%;
+        height: 100%;
+        min-width: auto;
+        min-height: auto;
+        vertical-align: bottom;
+        object-fit: contain;
+      }
+    }
+
+    &__count {
+      display: block;
+      min-width: 9px;
+      font-size: 13px;
+      font-weight: 500;
+      text-align: center;
+      margin-left: 6px;
+      color: $darker-text-color;
+    }
+
+    &:hover,
+    &:focus,
+    &:active {
+      background: lighten($ui-base-color, 16%);
+      transition: all 200ms ease-out;
+      transition-property: background-color, color;
+
+      &__count {
+        color: lighten($darker-text-color, 4%);
+      }
+    }
+
+    &.active {
+      transition: all 100ms ease-in;
+      transition-property: background-color, color;
+      background-color: mix(lighten($ui-base-color, 12%), $ui-highlight-color, 90%);
+
+      .reactions-bar__item__count {
+        color: $highlight-text-color;
+      }
+    }
+  }
+
+  .emoji-picker-dropdown {
+    margin: 2px;
+  }
+
+  &:hover .emoji-button {
+    opacity: 0.85;
+  }
+
+  .emoji-button {
+    color: $darker-text-color;
+    margin: 0;
+    font-size: 16px;
+    width: auto;
+    flex-shrink: 0;
+    padding: 0 6px;
+    height: 22px;
+    display: flex;
+    align-items: center;
+    opacity: 0.5;
+    transition: all 100ms ease-in;
+    transition-property: background-color, color;
+
+    &:hover,
+    &:active,
+    &:focus {
+      opacity: 1;
+      color: lighten($darker-text-color, 4%);
+      transition: all 200ms ease-out;
+      transition-property: background-color, color;
+    }
+  }
+
+  &--empty {
+    .emoji-button {
+      padding: 0;
+    }
+  }
+}