GLTF document loader selectively toggle model data

The vtkGLTFDocumentLoader learned to selectively enable/disable loading of certain types of model data from the gltf file. The loader exposes the following new API:

• SetLoadAnimation(bool): Load animation keyframes (default: true)

• SetLoadImages(bool): Load model images (default: true)

• SetLoadSkinMatrix(bool): Load inverse bind matrices for model Skin (default: true)