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/Command.java
* @throws NotDefinedException
	 *             If the command you are trying to execute is not defined.
	 * @throws NotEnabledException
	 *             If the command you are trying to execute is not enabled.
	 * @throws NotHandledException
	 *             If there is no handler.
	 * @since 3.2
	 */
	public final Object executeWithChecks(final ExecutionEvent event)
			throws ExecutionException, NotDefinedException,
			NotEnabledException, NotHandledException {
		firePreExecute(event);
		final IHandler handler = this.handler;
		if (!isDefined()) {
			final NotDefinedException exception = new NotDefinedException(
					"Trying to execute a command that is not defined"); 
			fireNotDefined(exception);
			throw exception;
		}
		
		if ((handler != null) && (handler.isHandled())) {
			if (!isEnabled()) {
				final NotEnabledException exception = new NotEnabledException(
						"Trying to execute a disabled command"); 
				fireNotEnabled(exception);
				throw exception;
			}
			try {
				final Object returnValue = handler.execute(event);
				firePostExecuteSuccess(returnValue);