modified game class hiearchy, turned off blending

-removed Background class
-created Collideable interface that all collideable objects should inherit
-created SceneObject class which all environment/scenery objects that
won't be interactive should inherit
-GameObject class objects should always be interactive, otherwise they
should inherit the SceneObject class

-added GenericSceneObject class that will represent any image in the
background
-added Ground class that represents a object that will act as the ground
-added a bitmap for the ground "ground.bmp"

-GameState now incorporates basic collision detection