Add client_get_by_groupid in remote library

Hello,

I searched inside the code of the API and I didn't find a function that returns the client from the group ID. Note that The contrary is possible with client_get_groupid.

I wrote an implementation in interface/lib/classes/remote.d/client.inc.php:

        public function client_get_by_groupid($session_id, $group_id)
        {
                global $app;
                if(!$this->checkPerm($session_id, 'client_get_id')) {
                        throw new SoapFault('permission_denied', 'You do not have the permissions to access this function.');
                        return false;
                }

                $group_id = $app->functions->intval($group_id);

                $rec = $app->db->queryOneRecord("SELECT client_id FROM sys_group WHERE groupid = ?", $group_id);
                if(isset($rec['client_id'])) {
                        $client_id = $app->functions->intval($rec['client_id']);
                        return $this->client_get($session_id, $client_id);
                } else {
                        throw new SoapFault('no_group_found', 'There is no client for this group ID.');
                        return false;
                }

        }

I didn't know how to handle the checkPerm, so I copy/past from client_get_id.