[Refactoring] Changed AUnit Hierachy,

0. ImageObj -> DrawableObj : Now Implements IDrawable
1. Animatable : Extends DrawableObj, implements IAnimatable
2. AUnit      : Extends AnimatableObj, implements IUnit
3. CustomView & Thread becomes AnimatableObj's subclass with container.
4. Anyway, AnimatableSurfaceView controlls surfaceView that has
"AnimatableObj"s.