…ository.

Make sure exported symbols are correctly set in __init__.py with __all__.
Renamed pytest fixture for creating a k8s namespace from ns to namespace since ns is a bit overloaded, especially in test_controller.py
Introduce typehints in controller.py and test_controller.py to massively improve developer experience (previously, one just really had to guess what functions are for and which types are expected)
Removed unused function parameters
Made function headers (i.e. parameter [type] defintion) compatible with what `kopf.on.[create/change/...]' expects
Introduce mypy (and missing stubs of external packages if available)
Introduce mypy ignores for (still) untyped parts of the codebase for now

…untyped external calls