The format property of Model resources is not being exported

[vincentmarchetti]

At release 1.0.0, the format property of model resources is being exported as an empty string.

Example fragment from the manifest produced for the demo video:

 "source": {
"id": "https://spri-open-resources.s3.us-east-2.amazonaws.com/iiif3dtsg/woodblocks/blueI.glb",
"format": "",
 "type": "Model"
}

Correct behavior for this example would be a value of "model/gltf-binary"

[vincentmarchetti]

A fix to this issue is in branch https://github.com/vincentmarchetti/iiif_3d_blender_plugin/tree/fix-format-export

Need to test for various combinations of:
-- the model id does not have a recognizable extension for a supported 3D format
-- the Content-Type header for the download does not have a supported 3D mimetype
The logic in this case will be to try the model/gltf-binary mime type, and add this to the model resource for export if the resource is successfully imported into Blender

If this works out, this code fix will be submitted as a PR