Please adopt custom VR URL

Please make VR URL customisable in manifest.yaml of app add:
`inputs:
              apikey: $API_KEY
              version: $VERSION
              vr_url: $VR_URL`
In serverless/image_processing_vr.js
`const visualRecognition = new VisualRecognitionV3({
    version: params.version,
    iam_apikey: params.apikey,
    url: params.vr_url
  });`