PBR parametres fix and expand

JME PBR has incorrect fresnel parametres setting. It has to be fixed in order to get correct shading.

This is not a request to JME developers, i believe we can have some custom fresnel setups in SSE, so that we can easily change dielectric behavior.

So, SSE need to have extracted PBR parametres, where fresnel takes its settings from gradient ramp (as it presented in valve's source engine)