fix revision count and drop observers

app/models/conference.rb

@@ -1,4 +1,5 @@
 class Conference < ActiveRecord::Base
+  include RevisionCount
   require 'uri'
   serialize :events_per_week, Hash
   # Needed to call 'Conference.with_role' in /models/ability.rb
@@ -734,6 +735,15 @@ class Conference < ActiveRecord::Base
     (start_hour..(end_hour - 1)).cover?(current_hour) ? current_hour - start_hour : 0
   end
 
+  ##
+  # Return the current conference object to be used in RevisionCount
+  #
+  # ====Returns
+  # * +ActiveRecord+
+  def conference
+    self
+  end
+
   private
 
   # Returns a different html colour for every i and consecutive colors are