Added starfield images for parallax
Added Background.java, a class to handle parallax effects in the background
Added background.png, the background
Modified Entity to make it abstract
Added background rendering to game
Added parallax offsets to Player class
Changed viewport width and height to static
Made playGameScreen a static instance, so it can be accessed from other classes without a lot of bother
Added enemyTexture.png
Created BaseProjectile class
Created BaseEnemy class