SsrFilter

Stand alone SSR filter for jMonkeyEngine3

Based on https://github.com/riccardobl/SimpleSSRShader

Essentially same as in this PR: jMonkeyEngine/jmonkeyengine#1144

I thought this might be an easier way for people to get the filter and improve it.

It's dependent on a PreNormalGloss pass defined in PBRLighting.j3md:

Technique PreNormalGlossPass {

    VertexShader GLSL100 :   MatDefs/SSR/normal_gloss.vert
    FragmentShader GLSL100 : MatDefs/SSR/normal_gloss.frag

    WorldParameters {
        WorldViewProjectionMatrix
        WorldViewMatrix
        WorldMatrix
        NormalMatrix
        ViewProjectionMatrix
        ViewMatrix
    }

    Defines {
        NUM_BONES : NumberOfBones
        INSTANCING : UseInstancing
        NUM_MORPH_TARGETS: NumberOfMorphTargets
        NUM_TARGETS_BUFFERS: NumberOfTargetsBuffers
        NORMALMAP : NormalMap
        ROUGHNESSMAP : RoughnessMap
        SPECGLOSSPIPELINE : UseSpecGloss
        GLOSSINESSMAP : GlossinessMap
    }

}

I didn't want to include the whole modified PBRLighting due to possible conflicts(?).

Demo here:

https://youtu.be/YxgEYg1D06Y