Revert "[IMP] user_story: Adding task in the user story will add it at the top of the list."

Created by: zaoral

Fix Vauxoo/instance#273 Close Vauxoo/instance#275 Reverts Vauxoo/addons-vauxoo#594

The change made generate a functional error using user story: make the task list editable in the embedded tree view and we do not want this:

We want to get inside the task to edit it all. Sorry for the trouble

Best Regards