Adding new ports does not refresh existing instances

[McManning]

Via #57 - when assets are reloaded and new ports have been introduced to the node script, the new ports are not added to existing node instances.

It may not need to serialize empty connections to new ports to all existing graph assets, which would probably make sense from a performance standpoint. But it should at the very least introduce the new ports when you open the editor for a graph (or an existing editor is refreshed).

I'm also wondering if it just makes sense to introduce a general purpose "graph fixer" either via an editor window for interactive corrections (again, possibly to resolve some issues with #57) or a broad stroke algorithm that runs through all graph assets and adds/removes ports, signals errors, changes behaviour references, etc.

I have an old ticket #20 that goes into the various problem cases in depth as well.