deep validation of open json scene

[kfarr]

As a user opening a 3dstreet scene from json I want to know that it was able to load all entities correctly.

There was a change starting to do this on 3dstreet-editor repo here: https://github.com/3DStreet/3dstreet-editor/tree/add-notify-messages

The changes should be made on this 3dstreet repo first and on console first to confirm working. Alternative to using this for notification messages is this could be displayed to end-user as a percentage completion bar as loading and placing entities progresses.