[FIX] stock: groups mixup in views

Use group_production_lot for serial options, group_stock_packaging for packaging, use group_tracking_lot for pallet/parcel
Groups are removed completly from the view for stock.tracking as they render the view useless.

Always display weights on the product form
They really have nothing to do with the logistic units and we don't have another group to restrict them to.

Fixes #1443
Merge branch '7.0' of https://github.com/odoo/odoo into 7.0-linux64