[acl] Possibility to override ACL PermissionGrantingStrategy

This class should be overridable.
An example, isFieldGranted don't check if isGranted, sometimes you need that :

class PermissionGrantingStrategy extends BasePermissionGrantingStrategy
{
    public function isFieldGranted(AclInterface $acl, $field, array $masks, array $sids, $administrativeMode = false)
    {
        try{
            return parent::isFieldGranted($acl, $field, $masks, $sids, $administrativeMode);
        }catch (NoAceFoundException $noFieldAces){
            return $this->isGranted($acl,$masks,$sids,$administrativeMode);
        }
    }
}