QtToolBarManager::restoreState(): support ignoring actions that are not part of the state being restored

QtToolBarManager::restoreState() removes the old actions when restoring a state. This also removes new actions that are added before the old state is restored, and which are not part of the old state.

It therefore becomes unnecessarily difficult to introduce new actions, for example in a new version of an application, without having to reset the tool bar states and start from scratch. Otherwise the new actions have to be added after the old state has been restored.

It would therefore be nice if QtToolBarManager::restoreState() supported ignoring any actions that are not part of the old state being restored, so that old actions are still restored as per usual, but the new actions are still kept in the tool bar and not removed.