make comment and thread inherited from a single class

models/comment.rb

@@ -1,5 +1,6 @@
-class Comment
-  include Mongoid::Document
+require_relative 'content'
+
+class Comment < Content
   include Mongoid::Tree
   include Mongo::Voteable
   include Mongoid::Timestamps

models/comment_thread.rb

@@ -1,5 +1,6 @@
-class CommentThread
-  include Mongoid::Document
+require_relative 'content'
+
+class CommentThread < Content
   include Mongo::Voteable
   include Mongoid::Timestamps
 

models/content.rb

@@ -0,0 +1,4 @@
+class Content
+  include Mongoid::Document
+  
+end