g3d Model additional attributes

- Additional textures : ambient, emissive, reflection, unknown.
"Unknown" make sure that all all textures can be accessed by at least a
custom shader.

binding (sampler2D) :
u_ambientTexture
u_reflectionTexture
u_emissiveTexture

- Texture translation and scaling for diffuse and specular textures.

binding (vec2) :
u_diffuseUVTranslation
u_diffuseUVScaling
u_specularUVTranslation
u_specularUVScaling