added gltf 2.0 input to geometryc

Preferred output coordinate system transformation added.

glTF2.0 is tested with all models from https://github.com/KhronosGroup/glTF-Sample-Models/tree/master/2.0

Static mesh output looks ok for all of them, but as output file format hasn't changed only static mesh is exported. No animation, nodes, materials. etc.

Author: attilaz