code: public App clearSettings() {
  		// remove the old settings one at a time so the remove setting listeners are invoked
  		if (settings != null && !settings.isEmpty()) {
  			List<String> keysToRemove = settings.keySet().stream().collect(Collectors.toList());
  			keysToRemove.stream().forEach(oldKey -> removeSetting(oldKey));
  		}
  		return this;
  	}
docs: Clears all app settings and invokes each {@link AppSettingRemovedListener}s.
  @return this