add metadata component to scene

[kfarr]

this should be the "source of truth" for the title and id of a scene, perhaps other metadata in the future

• component name metadata
• 2 property fields: "sceneTitle", "sceneId" both strings
• this is added to scene by loaders, it is not manually added to a scene

By default the fields are null or empty string

• Streetmix loader should fill in sceneTitle field using streetmix street name ONLY IF the sceneTitle field is empty
• 3DStreet JSON loader should overwrite the current scene name when loading a new scene, and load the sceneId from the corresponding field in the document, or set the sceneId to null or empty string if none specified
• 3DStreet cloud load (from open dialog) should overwrite the current sceneTitle name when loading a new scene as well as the sceneId (this is on 3dstreet-editor repo side, can ignore for this 3dstreet core ticket)

Example of future property fields:

• createdTimestamp, editedTimestamp, etc.

This will be used by editor for 3DStreet/3dstreet-editor#261 and 3DStreet/3dstreet-editor#275

[kfarr]

wip #346

[kfarr]

closed by #346