support listing availlable scripts in pixl.

js/pixl/public/index.html

            }
            xhr.send();
        };
        pixl.scripts.list = function() {
            var xhr = new XMLHttpRequest();
            xhr.open('GET', '/scripts');
            xhr.onreadystatechange = function() {
                if (xhr.readyState == 4) {
                    var scripts = xhr.responseText.split("\n");
                    for (var i = 0; i < scripts.length; i++) {
                        console.log(scripts[i]);
                    }
                }
            };
            xhr.send();
        }
    </script>
</body>
</html>