ClassFinder:
Removed exclude argument, which is basically covered with
obj.__module__ == module.__name__ which ensures that no imported
classes are found, which was the only use case for exclude.
This didn't change the public "API" used by modules.
.core.io contains the IO classes, namely IOHandler, StandaloneIO and JSONIO
.core.util contains SettingsBase and ClassFinder
.core.exceptions contains all custom exceptions
