add Scroller.hx : scrolling image with custom direction and custom speed

Usage : 

var scroller:Scroller = new Scroller(atlas, "wanted_img", speed, move_on_x, move_on_y);
scene.add(scroller);
scroller.init();
scroller.play();


Can stop Scroller : 

scroller.stop();

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atlas must be a TextureAtlas containing the "wanted_img".
move_on_x and move_on_y can be any value. They are multiplied by the given speed to scroll the image.