mvvmfx-utils/src/main/java/de/saxsys/mvvmfx/utils/listener/ListenerManager.java
private <T, U> void clearMap(Map<T, Set<U>> map, BiConsumer<T, U> consumer) {
		for (T observable : map.keySet()) {
			for (U listener : map.get(observable)) {
				consumer.accept(observable, listener);
			}
		}
		map.clear();
	}
private <T, U> void clearMap(Map<T, Set<U>> map, BiConsumer<T, U> consumer) {
		for (T observable : map.keySet()) {
			for (U listener : map.get(observable)) {
				consumer.accept(observable, listener);
			}
		}
		map.clear();
	}
This method is used to clear the given map. To do this you need to implement a BiConsumer that calls the specific
method to remove a listener from an observable.

This needs to be done as there is no common interface with a remove method that all types of observables are
implementing. Therefore the method call to the specific removeListener method needs to be done in an extra
function.

@param map
the multimap that contains the observables and listeners.
@param consumer
a function that calls the specific remove method for the given types.