Class Hierarchy
- java.lang.Object
- com.deco2800.game.physics.BodyUserData
 - com.deco2800.game.physics.PhysicsContactListener (implements com.badlogic.gdx.physics.box2d.ContactListener)
 - com.deco2800.game.physics.PhysicsEngine (implements com.badlogic.gdx.utils.Disposable)
 - com.deco2800.game.physics.PhysicsLayer
 - com.deco2800.game.physics.PhysicsService
 - com.deco2800.game.physics.PhysicsUtils