Rewrote the osgbillboard demo so that it creates a point rotatated billbaord
and X,Y and Z axis billboards to both test and demonstrate this types of
billboards in action.
is orientated towards the viewer.
Changed the lightmodel ambient level to 0.1,0.1,0.1 instead of 0.0, so that
a small amount of ambient lighting is available to render back surfaces.
The osgreflect and osgprerender suffered unexpected behaviors because of
no lighting on the backfaces.
