add the feature that FBX-conv can handle LayeredTexture
add the feature that FBX-conv can handle LayeredTexture

cocos2d-x/fbx-conv,lvlonggame/fbx-conv,cocos2d-x/fbx-conv,cocos2d-x/fbx-conv,super626/fbx-conv,super626/fbx-conv,lvlonggame/fbx-conv,lvlonggame/fbx-conv,super626/fbx-conv