added ScrollingHandler to handle the backgrounds / scrollables,
edited MainState, edited Sprite, added hill images, created GreenHills and BackHills classes for the first level
works infinitely with collision
Merge branch 'dev' of https://github.com/tinhtooang/balloonatic into dev

Conflicts:
	src/game/MainState.java
	src/graphic/Balloon.java
	src/graphic/SceneObject.java
	src/graphic/Sprite.java