[FIX] odoo.py fix fetching of git remotes

remove the useless heads in local refs so that:

git checkout -b master odoo/master

and

git checkout -b master-name odoo-dev/master-name

works.
[FIX] website_sale perfomance on public categories

Use a domain instead of python filtering when loading root categories.

Closes #4324
[FIX] payment_buckaroo: copy values dict to avoid altering original dict

_buckaroo_generate_digital_sign uses the values dict to generate the shasign
At some point, it alters the dict, it removes BRQ_SIGNATURE, but, as the values dict was not copied, it altered the original dict.
So, the key BRQ_SIGNATURE was not anymore present for methods called after _buckaroo_generate_digital_sign.
For instance, the overriden method form_feedback of website_sale payment
Merge branch '8.0' of https://github.com/odoo/odoo into 8.0-win32