Add quick links to the admin interface in the WebUI (#8545)

* Allow to show a specific status in the admin interface

* Let the front-end know the current account is a moderator

* Add admin links to status and account menus

If the current logged-in user is an admin, add quick links to the admin
interface in account and toot dropdown menu. Suggestion by @ashkitten

* Use @statuses.first instead of @statuses[0]

app/controllers/admin/statuses_controller.rb

@@ -22,6 +22,15 @@ module Admin
       @form     = Form::StatusBatch.new
     end
 
+    def show
+      authorize :status, :index?
+
+      @statuses = @account.statuses.where(id: params[:id])
+      authorize @statuses.first, :show?
+
+      @form = Form::StatusBatch.new
+    end
+
     def create
       authorize :status, :update?