3D BillBoard

Add BillBoard and BillBoardTest.
BillBoard are mostly transparency so add a transparency queue in the render.

static class variable can work. 
But I think this variable has nothing to do with the class, It is only used in this function, and I do not want to construct it each call. Maybe you can use another algorithm without this variable in future.
We can make it as class variable if static variable here is not allowed.