New class GraphicObject.

The created and bounded to Unit and Player, i.e. the lifetime is the
same. All objects that is a MovingObject will be drawn by GraphicObject.
Removed unused class.

Plus added some filter to make the project more manageable.
Make use of class Graphicobject.

All movingobjects is now bound to a an instance of GraphicObject to
handle the drawing of the object. No use of GraphicTask anymore.
removeBody moved to destructor.

In all Objects.
Moving objects is now deleted when they die.

Added a callback in zombiebehavior to signal when a target dies so that
the reference to target is not used.