- Update the canvas graph generation to flag its uploaded init and mask images as `intermediate`.
- During canvas setup, hit the update route to associate the uploaded images with the session id.
- Organize the socketio and RTK listener middlware better. Needed to facilitate the updated canvas logic.
- Add a new action `sessionReadyToInvoke`. The `sessionInvoked` action is *only* ever run in response to this event. This lets us do whatever complicated setup (eg canvas) and explicitly invoking. Previously, invoking was tied to the socket subscribe events.
- Some minor tidying.
