Added self-destructing/expiring statuses

• Added:
- self-destructing/expiring statuses for GabPRO members only
- ExpiringStatusWorker
- stopwatch icon
- expires_at redux values
- expires_at button in composer
- expires at selection popover

• Updated:
- Schedule status button to not show if expiring status active

app/serializers/rest/status_serializer.rb

@@ -4,7 +4,7 @@ class REST::StatusSerializer < ActiveModel::Serializer
   attributes :id, :created_at, :revised_at, :in_reply_to_id, :in_reply_to_account_id,
              :sensitive, :spoiler_text, :visibility, :language,
              :uri, :url, :replies_count, :reblogs_count,
-             :favourites_count, :quote_of_id
+             :favourites_count, :quote_of_id, :expires_at
 
   attribute :favourited, if: :current_user?
   attribute :reblogged, if: :current_user?