Pyreverse: Add option to ignore classes without relationships

[nickdrozd]

Current problem

Class diagrams are great for understanding the relationships between classes. But the class diagrams produced by Pyreverse include all classes, including those that have no relationships. Those objects clutter the diagrams.

In this example, there are seven unconnected nodes:

Desired solution

It would be nice to have an option to exclude unconnected classes from the class diagram. With the option enabled, Pyreverse would only display classes that have some kind of relationship to other classes.

Additional context

Maybe the package diagram too?

[nickdrozd]

The same diagram without the stray nodes: