Support custom ActionListeners for Command Buttons

In some scenarios you show a dialog which displays a progress of a background task. If those dialogs have a cancel button it should signal the background task to stop and the dialog should remain open till the background task terminates. Currently not possible without dirty hacks.
You can add a PropertyChangeListener for the TaskDialog result, but you can not wait in EDT for the termination of the background task, therefore a new Thread has to be created that closes the dialog when the background task terminates, but once the result changes to a result that is marked as "closing" (see TaskDialogContent.CommandAction.actionPerformed(ActionEvent) ) the dialog will disappear.