Save-upload functionality

On save we get from Dynamo all workspaces that were loaded - home workspace (ws) and all custom nodes' workspaces.

We can load file of home ws (*.dyn) or custom node ws (*.dyf). 

New concept here is proxy node. It's a custom node that hasn't its own definition (corresponding ws). If we load a ws with a custom node instance before we load custom node definition this node will be marked as proxy. Then after loading the custom node' ws this node will stop being proxy.
This is confusing for users and appears to be more for debugging purposes.  No need to surface this in the UI - I'd just remove this.