refactored detection of texture sizes for cubemaps
removed the assumption that if we give U32 GFXTextureManager::getTextureDownscalePower( GFXTextureProfile *profile ) no profile, it should go right ahead and downscale anyway
sniped the downscaling strings in the resulting U32 getProbeTexSize(); and void setCubeTexSize(const U32 cubemapFaceSize); until sucj time as we can properly follow up all possible combinations of shiping in one scale, and a customer choosing to use lower resolution textures as the current result is a hard shutoff entirely