Compass: Removed color/color2 fields
Graphics: Replaced fillOval() by fillCircle()
Clock: Moved ClockObserver interface into Clock class
EventManager: Moved EventInterface interface into EventManager class
EventManager: Cleanup and simplifications
Obj3dManager: Simplified loops in sortObjects() method
Obj3dManager: Use Collections.sort() in sortObjects() with custom Comparator
Obj3dManager: Extracted ObjectLayer class