journal不应该算入ForgeActivity，历史数据应该删除

db/migrate/20151218022014_batch_delete_project_journal_activities.rb

@@ -0,0 +1,9 @@
+# encoding: utf-8
+class BatchDeleteProjectJournalActivities < ActiveRecord::Migration
+  def up
+    ForgeActivity.where('forge_act_type = \'Journal\'').destroy_all  #需要触发回调
+  end
+
+  def down
+  end
+end