save the created cell in a dict and give the dict to the newCell method.

That's more simple and in this way, it's make possible the caclulation script
to return other things than quantity and price (categories for example).


git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@18292 20353a03-c40f-0410-a6d1-a30d3c3de9de