Bug 126414 [Commands] handlers: Provide help context ids
For commands and handlers to replace actions, they need to be capable of providing help context identifiers. For an example, see OpenResourceHandler in org.eclipse.ui.ide. This help context id will need to be definable through XML and through code.
bundles/org.eclipse.core.commands/src/org/eclipse/core/commands/CommandManager.java
*            The listener to attach; must not be <code>null</code>.
	 */
	public final void addExecutionListener(final IExecutionListener listener) {
		if (listener == null) {
			throw new NullPointerException(
					"Cannot add a null execution listener"); 
		}
		if (executionListeners == null) {
			executionListeners = new ListenerList(ListenerList.IDENTITY);
			
			executionListener = new ExecutionListener();
			final Iterator commandItr = handleObjectsById.values().iterator();
			while (commandItr.hasNext()) {
				final Command command = (Command) commandItr.next();
				command.addExecutionListener(executionListener);
			}
		}
		executionListeners.add(listener);
	}
	/*
	 * (non-Javadoc)
	 * 
	 * @see org.eclipse.core.commands.ICategoryListener#categoryChanged(org.eclipse.core.commands.CategoryEvent)
	 */
	public final void categoryChanged(CategoryEvent categoryEvent) {
		if (categoryEvent.isDefinedChanged()) {
			final Category category = categoryEvent.getCategory();
			final String categoryId = category.getId();
			final boolean categoryIdAdded = category.isDefined();
			if (categoryIdAdded) {