[update] Compine Snake Head and Snake Body object into Snake Part object

[update] Snake Part objects become first in first out instead of regenerate in every reflesh, GREAT!
[update] Modify Drawing code by using William's direction
[update] Saperate screen update and game update, they can have different speed now
[update] Moving snakeMove into gameUpdate, so snake movement follow gameUpdate speed now
[update] Adding Update function into each onscreen game object, so they can do update during the game easily