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
* @see Command
	 */
	public final Command getCommand(final String commandId) {
		checkId(commandId);
		Command command = (Command) handleObjectsById.get(commandId);
		if (command == null) {
			command = new Command(commandId);
			handleObjectsById.put(commandId, command);
			command.addCommandListener(this);
			if (executionListener != null) {
				command.addExecutionListener(executionListener);
			}
		}
		return command;
	}
	/**
	 * Returns the categories that are defined.
	 * 
	 * @return The defined categories; this value may be empty, but it is never
	 *         <code>null</code>.
	 * @since 3.2
	 */
	public final Category[] getDefinedCategories() {
		final Category[] categories = new Category[definedCategoryIds.size()];
		final Iterator categoryIdItr = definedCategoryIds.iterator();
		int i = 0;
		while (categoryIdItr.hasNext()) {
			String categoryId = (String) categoryIdItr.next();
			categories[i++] = getCategory(categoryId);
		}