Improve Responder node workflow

[Hoikas]

Work toward deprecating the Responder State node and move toward implicit responder states built from command linkage. This will ideally make the logic node tree easier to follow. Will also need to build in a framework for detecting deprecated node types on load and upgrading them on-the-fly. But that shouldn't be too hard.

[Hoikas]

After discussion with @Deledrius, we determined that responder states need to remain part of the workflow because these are referenced in Python's ptAttribResponders. However, we may want to consider removing responder command nodes and making message nodes single-user. To indicate command waits, waitable messages can send other messages.