Move all order logic to models

- Have a default order for each model
-- The overall default is ID DESC
- Allow for custom orderings
-- When comma-separated IDs are used

app/logical/post_query_builder.rb

@@ -515,6 +515,11 @@ class PostQueryBuilder
     when "rank"
       relation = relation.order("log(3, posts.score) + (extract(epoch from posts.created_at) - extract(epoch from timestamp '2005-05-24')) / 35000 DESC")
 
+    when "custom"
+      if q[:post_id].present? && q[:post_id][0] == :in
+        relation = relation.find_ordered(q[:post_id][1])
+      end
+
     else
       relation = relation.order("posts.id DESC")
     end