fix revision count and drop observers

db/migrate/20170108053041_add_default_to_revision_in_conference.rb

@@ -0,0 +1,5 @@
+class AddDefaultToRevisionInConference < ActiveRecord::Migration
+  def change
+    change_column :conferences, :revision, :integer, default: 0, null: false
+  end
+end

db/schema.rb

@@ -90,7 +90,7 @@ ActiveRecord::Schema.define(version: 20170629232817) do
     t.datetime "created_at"
     t.datetime "updated_at"
     t.string   "logo_file_name"
-    t.integer  "revision"
+    t.integer  "revision",           default: 0,     null: false
     t.boolean  "use_vpositions",     default: false
     t.boolean  "use_vdays",          default: false
     t.boolean  "use_volunteers"