This is an example of using the siteconfig decorator for adding a sitewide quicklinks navigation

_config.php

<?php

Object::add_extension('SiteConfig', 'QuickLinksSiteConfig');

navigation.ss

<ul class="inline-block">
	<% loop SiteConfig.QuickLinks %>
	<li><a href="$Link" <% if OnClick %>onclick="$OnClick.XML" <% end_if %><% if AccessKey %>accesskey="$AccessKey.XML" <% end_if %>alt="$AltText.XML" class="arrow">$Title</a></li>
	<% end_loop %>
</ul>

QuickLink.php

<?php

class QuickLink extends DataObject {

    public static $has_one = array(
		'SiteConfig' => 'SiteConfig'
	);
    
     /**
     *
	 * @var array
	 */
	public static $db = array(
		'Order' => 'Int',
		'AccessKey' => 'Int',
		'OnClick' => 'Varchar(255)'
	);

	/**
	 *
	 * @var array
	 */
	public static $has_one = array(
		'Page' => 'Page'
	);

	/**
	 *
	 * @var array
	 */
	public static $summary_fields = array(
		'PageID' => 'Page',
		'AccessKey' => 'Access key',
		'OnClick' => 'OnClick'
	);

	/**
	 * Sort the links by the Order fields
	 *
	 * @var string
	 */
	public static $default_sort = 'Order';

	/**
	 *
	 * @return FieldList
	 * @codeCoverageIgnoreStart
	 */
	public function getCMSFields() {
		$fields = new FieldList();
		$fields->push(new TabSet("Root", $mainTab = new Tab("Menu")));
		$fields->addFieldToTab("Root.Menu", new TreeDropdownField('PageID', 'Link to', 'Page'));
		$fields->addFieldToTab('Root.Menu', $accessKey = new TextField('AccessKey', 'AccessKey (optional)'));
		$fields->addFieldToTab('Root.Menu', $onclick = new TextField('OnClick', 'On click event (optional)'));
		$onclick->setDescription("Ex. _gaq.push(['_trackEvent', window.location.pathname, 'Footer-BankingInfo', 'text-link/Mortgage calculators']);");
		return $fields;
	}
	// @codeCoverageIgnoreStop

	/**
	 *
	 * @return string
	 */
	public function getTitle() {
		return $this->Page()->Title;
	}

	/**
	 *
	 * @return string
	 */
	public function getMenuTitle() {
		return $this->Page()->MenuTitle;
	}

	/**
	 *
	 * @return string
	 */
	public function getLink() {
		return $this->Page()->Link();
	}

	/**
	 *
	 * @return string
	 */
	public function getAltText() {
		return $this->Page()->MenuTitle;
	}
}

QuickLinksSiteConfig.php

<?php
/**
 * Adds fields to the global settings
 *
 * @package SiteConfig
 */
class QuickLinksSiteConfig extends DataExtension {

    /**
	 * Extra static fields to add to the SiteConfig object
	 *
	 * @var Array
	 */
	public static $has_many = array(
		'QuickLinks' => 'QuickLink'
	);

	/**
	 * Adds form fields to the CMS settings page for each of the extra static fields
	 *
	 * @param FieldList $fields The list of fields defined in the parent class SiteConfig
	 */
	public function updateCMSFields(FieldList $fields) {
		$config = new GridFieldConfig();
		$config->addComponent(new GridFieldToolbarHeader());
		$config->addComponent($sort = new GridFieldSortableHeader());
		$config->addComponent(new GridFieldInlineEditing());
		$config->addComponent(new GridFieldButtonRow('before'));
		$config->addComponent($addButton = new GridFieldAddNewButton('buttons-before-left'));
		$addButton->setButtonName('Add quicklink');
		$config->addComponent(new GridFieldDeleteAction());
		$config->addComponent(new GridFieldEditButton());
		$config->addComponent(new GridFieldDetailForm());
		$config->addComponent(new GridFieldSortableRows('Order'));

		$gridField = new GridField('Quicklink', 'QuickLinks', $this->owner->QuickLinks(), $config);
		$fields->addFieldToTab('Root.QuickLinks', $gridField);
	}
}