[glTF] URI-decode all URIs present in a glTF model

[dmnsgn]

A new sample model has been added to test URI: https://github.com/KhronosGroup/glTF-Sample-Models/tree/master/2.0/Box%20With%20Spaces

Our implementation will fail: https://github.com/pex-gl/pex-renderer/blob/18746d1869dc11c9ca2bcff1eaaad428cd9b98e7/loaders/glTF.js#L937

Fix:

url: decodeURIComponent([basePath, image.uri].join('/')),

[vorg]

I did have issues with spaces, so thats good catch