Reset cell key to None in REQUEST if no cell value; Validate subfields for...

Reset cell key to None in REQUEST if no cell value; Validate subfields for editable cells. FIXME: currently only keys which contains a cell value are validated

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@6826 20353a03-c40f-0410-a6d1-a30d3c3de9de