[MERGE] [IMP] product: product and product template management

[MERGE] [IMP] product: product and product template management

product
- added a is_only_child field, telling whether the product is the only child of its template
- form view: fields coming from the template are now readonly when there are several products (variants) for the template; added a link to the template on the product form view
- renamed Products menu into All Products
- some improvements in search view, notably groupby

product.template
- improved form view to look more similar to the product one
- added Product Template menus when using variants

website_sale: do not fetch templates without products

bzr revid: tde@openerp.com-20140122183759-s9lfvfeo8f6ytm34