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
* Notifies all of the listeners to this manager that the set of defined
	 * command identifiers has changed.
	 * 
	 * @param event
	 *            The event to send to all of the listeners; must not be
	 *            <code>null</code>.
	 */
	private final void fireCommandManagerChanged(final CommandManagerEvent event) {
		if (event == null)
			throw new NullPointerException();
		final Object[] listeners = getListeners();
		for (int i = 0; i < listeners.length; i++) {
			final ICommandManagerListener listener = (ICommandManagerListener) listeners[i];
			listener.commandManagerChanged(event);
		}
	}
	/**
	 * Returns all of the commands known by this manager -- defined and
	 * undefined.
	 * 
	 * @return All of the commands; may be empty, but never <code>null</code>.
	 */
	public final Command[] getAllCommands() {
		return (Command[]) handleObjectsById.values().toArray(
				new Command[handleObjectsById.size()]);
	}
	/**
	 * Gets the category with the given identifier. If no such category
	 * currently exists, then the category will be created (but be undefined).
	 *