FEATURE: Shared Drafts

This feature can be enabled by choosing a destination for the
`shared drafts category` site setting.

* Staff members can create shared drafts, choosing a destination
category for the topic when it is published.

* Shared Drafts can be viewed in their category, or above the
topic list for the destination category where it will end up.

* When the shared draft is ready, it can be published to the
appropriate category by clicking a button on the topic view.

* When published, Drafts change their timestamps to the current
time, and any edits to the original post are removed.

app/serializers/topic_list_serializer.rb

@@ -8,15 +8,21 @@ class TopicListSerializer < ApplicationSerializer
              :for_period,
              :per_page,
              :top_tags,
-             :tags
+             :tags,
+             :shared_drafts
 
   has_many :topics, serializer: TopicListItemSerializer, embed: :objects
+  has_many :shared_drafts, serializer: TopicListItemSerializer, embed: :objects
   has_many :tags, serializer: TagSerializer, embed: :objects
 
   def can_create_topic
     scope.can_create?(Topic)
   end
 
+  def include_shared_drafts?
+    object.shared_drafts.present?
+  end
+
   def include_for_period?
     for_period.present?
   end