Consider task duration in ordergroup stats.

* Also added duration to task template in workgroup task_duration.

db/migrate/20110507192928_add_task_duration_to_workgroups.rb

@@ -0,0 +1,9 @@
+class AddTaskDurationToWorkgroups < ActiveRecord::Migration
+  def self.up
+    add_column :groups, :task_duration, :integer, :default => 1
+  end
+
+  def self.down
+    remove_column :groups, :task_duration
+  end
+end