[-] Core: ProductSale no more takes products with no visibility

Fixed bug that's ProductSale is taking products with no visibility, displaying them in module blockbestsellers. But as they have no visibility, we don't want to display them!
// some changes on admin customer view
Merge pull request #282 from DrySs/patch-1

[-] Core: ProductSale no more takes products with no visibility
Merge branch 'development' of https://github.com/PrestaShop/PrestaShop into development
[*] BO: add a save and stay button in CMS edit page

This button was missing to edit easily CMS pages.
Merge pull request #283 from DrySs/patch-2

[*] BO: add a save and stay button in CMS edit page
[-] Installer: Fix 2 path for the upgrader
[-] BO: fixed lots of UI bugs in CMS:
- no more id_category (doesn't exists, it's id_cms_category)
- change category position now redirects in parent category (not at root category)
- change category status now redirects in parent category (not at root category)
- delete multiples category now redirects in parent category (not at root category)
- add form new category now auto select parent category (not root category)
- add a new category now redirects in parent category (not at root category)
- delete multiple categories now redirects in parent category (not at root category)
- now execute parent::postProcess() only if none action found (duplicate postProcess was done)
- now redirects to CMS form if found errors (not at root category)
- fixed unexists $object variable (was $cms) for saveAndStay
- delete multiple cms content now redirects in parent category (not at root category)
- change cms content position now redirects in parent category (not at root category)
- change cms content status now redirects in parent category (not at root category)
Merge branch 'development' of https://github.com/PrestaShop/PrestaShop into development