Xith3DDefaults

hi

I added a new class called Xith3DDefaults to the com.xith3d package. It is supposed to hold some defaults for the whole library. So far I have added a debugging flag and the Node.defaultPickable property to it.

This global debuging property can be overruled by all classes. I have changed all classes having such a debug flag to make use of this new feature. Well, I have spared out your classes, croft. Could you please do this change to your classes, so that we are consistent?

Marvin