initial commit for stock_picking_update_date

It is green already, but I need to handle the stock.picking.in and out
and add some docs in __openerp__.py
allow to update the date on all picking types
update date: improve description
rename things as suggested
improve comments and tooltips
Merge pull request #10 from lepistone/7.0-add-update-date

7.0 add stock_picking_update_date