Illegal image formats in resulting GLTF file.

[vsantosu]

When converting a FBX to a GLTF file, either binary or JSON gltf, the script(fbx2gltf.py) should do image transformation to PNG or JPEG in order to support most rendering engines. To reproduce the bug, try to transform a FBX with reference to a TGA image.

[pissang]

Yes it will be useful. Didn't do it because it needs other image processing libraries like Pillow