Executable Model Configurator

This release inverts the relationship between the "model configurator" (i.e. - the rx.py file) and the library routines that interact with it.
Previously, the configurator was just an information store, which was a bit wasteful, since it is a Python file.
Now, the configurator is executable and drives the model configuration process, drawing upon the library functionality for assistance.
This change results in cleaner code logic and, I believe, makes more sense from the developer's perspective.