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

config/routes.rb

@@ -173,9 +173,12 @@ Rails.application.routes.draw do
         get :edit
       end
     end
+
     resources :email_domain_blocks, only: [:index, :new, :create, :destroy]
     resources :action_logs, only: [:index]
     resources :warning_presets, except: [:new]
+    resources :announcements, except: [:show]
+
     resource :settings, only: [:edit, :update]
 
     resources :invites, only: [:index, :create, :destroy] do
@@ -317,6 +320,16 @@ Rails.application.routes.draw do
       resources :scheduled_statuses, only: [:index, :show, :update, :destroy]
       resources :preferences, only: [:index]
 
+      resources :announcements, only: [:index] do
+        scope module: :announcements do
+          resources :reactions, only: [:update, :destroy]
+        end
+
+        member do
+          post :dismiss
+        end
+      end
+
       resources :conversations, only: [:index, :destroy] do
         member do
           post :read