[IMP] doc : add python idioms and odoo specific coding guidelines
[IMP] doc : add python idioms and odoo specific coding guidelines

- add python idioms
- odoo specific guidelines (for ORM, translations, ...) inspired from old guidelines v6.0
- some other best pratices

dfang/odoo,bplancher/odoo,bplancher/odoo,microcom/odoo,microcom/odoo,Elico-Corp/odoo_OCB,Elico-Corp/odoo_OCB,ygol/odoo,microcom/odoo,hip-odoo/odoo,microcom/odoo,bplancher/odoo,storm-computers/odoo,Elico-Corp/odoo_OCB,storm-computers/odoo,ygol/odoo,dfang/odoo,laslabs/odoo,hip-odoo/odoo,dfang/odoo,hip-odoo/odoo,dfang/odoo,microcom/odoo,ygol/odoo,ygol/odoo,laslabs/odoo,hip-odoo/odoo,storm-computers/odoo,hip-odoo/odoo,dfang/odoo,laslabs/odoo,laslabs/odoo,Elico-Corp/odoo_OCB,Elico-Corp/odoo_OCB,storm-computers/odoo,ygol/odoo,hip-odoo/odoo,laslabs/odoo,bplancher/odoo,storm-computers/odoo,dfang/odoo,ygol/odoo,bplancher/odoo,microcom/odoo,ygol/odoo,bplancher/odoo,Elico-Corp/odoo_OCB,laslabs/odoo,storm-computers/odoo