Support different content source types for a visualValue Resource

Current State

as visualValue we support for gltf and draco resources:

• base64 for gltf + draco
• web URL for draco

Example simple instance

const instanceTemplate = {
  "eClass": "SimpleInstance",
  "id": "ANeuron",
  "name": "The first SimpleInstance to be render with Geppetto Canvas",
  "type": { "eClass": "SimpleType" },
  "visualValue": {
    "eClass": GEPPETTO.Resources.GLTF,
    'gltf': neuron
  }
}

Change Proposal

We should generalize the way data is provided to a Simple Instance.

Two common ways that we should start with:

• by web URL
• by directly passing content as string (e.g. base64)

Extension of visualValue structure by a type and data attribute:

"visualValue": { “data”: “https://github.com” , “type”: DataType.URL, “eClass”: GEPPETTO.Resources.GLTF,}
"visualValue": { “data”: “encoded-string” , “type”: DataType.Base64, “eClass”: GEPPETTO.Resources.GLTF,}
"visualValue": { data: “encoded-string” , type: DataType.Base64, “eClass”: GEPPETTO.Resources.DRACO, }

No files or tests are named. Start by tracing how visualValue handles GLTF and DRACO resources, then verify that both web URLs and directly supplied strings are supported through the proposed type and data attributes.