[FIX] point_of_sale: chrome was dropping the cookie when loading the company logo, resulting in an incorrect logo in multi-db setups.
[FIX] mrp: force empty values for fields that were dropped

This ensures the field values are cleared during
upgrades from previous versions
[FIX] product,purchase,point_of_sale: force empty values for dropped fields

At 96f038a product-related fields were removed due
to an important product.template/product.product
refactoring. As the field values were simply
dropped, they may not be nullified when upgrading an
existing database. Forcing them to False will take
care of it.
Merge branch '8.0' of https://github.com/odoo/odoo into 8.0-linux64