Add bookmarks (#7107)

* Add backend support for bookmarks

Bookmarks behave like favourites, except they aren't shared with other
users and do not have an associated counter.

* Add spec for bookmark endpoints

* Add front-end support for bookmarks

* Introduce OAuth scopes for bookmarks

* Add bookmarks to archive takeout

* Fix migration

* Coding style fixes

* Fix rebase issue

* Update bookmarked_statuses to latest UI changes

* Update bookmark actions to properly reflect status changes in state

* Add bookmarks item to single-column layout

* Make active bookmarks red

app/serializers/rest/status_serializer.rb

@@ -9,6 +9,7 @@ class REST::StatusSerializer < ActiveModel::Serializer
   attribute :favourited, if: :current_user?
   attribute :reblogged, if: :current_user?
   attribute :muted, if: :current_user?
+  attribute :bookmarked, if: :current_user?
   attribute :pinned, if: :pinnable?
 
   attribute :content, unless: :source_requested?
@@ -93,6 +94,14 @@ class REST::StatusSerializer < ActiveModel::Serializer
     end
   end
 
+  def bookmarked
+    if instance_options && instance_options[:bookmarks]
+      instance_options[:bookmarks].bookmarks_map[object.id] || false
+    else
+      current_user.account.bookmarked?(object)
+    end
+  end
+
   def pinned
     if instance_options && instance_options[:relationships]
       instance_options[:relationships].pins_map[object.id] || false