Updated atmosphere renderer

Atmospheric scattering effects shader works:
* from space the atmo looks pretty correct.
* for now, earth must be centered at origin :/

Added code to allow for culling of front faces instead of back (required
for sky shader)

Need to:
* fix location issue (recalc vector math)
* add other shaders:
** sky from atmo
** space from atmo
** ground from space
** ground from atmo