Replace atexit with explicit module register/unregister methods

[keianhzo]

I usually get exceptions running test when calling atexit. This PRs replaces atexit with a more explicit register_module and unregister_module methods that will be called before the component class is registered to give the module a chance to register classes that the component might require but that need to be loaded before Blender's runtime calls the class' register/unregister methods.