function getMaterialData (data) {
  return {
    fog: data.fog,
    color: new THREE.Color(data.color),
    wireframe: data.wireframe,
    wireframeLinewidth: data.wireframeLinewidth
  };
}
Builds and normalize material data, normalizing stuff along the way.

@param {object} data - Material data.
@returns {object} data - Processed material data.