when both q/sforms are unknown. Otherwise should default to
nibabel. Also added method to MelodicClassification to return all labels.

multiple topics to be specified.

instead of props.

given topic.

passed through to listener functions.

a warning if the sub-class is also a HasProperties, because both classes
define a 'notify' method, which could be super confusing.

anymore, and might get deleted.

fixing it anyway.

of lenght 1.

instanceified. Image.isNeurological is now memoized.

immediatelly re-run the idle loop.