Implement model record links

I see that this isn't exactly consistent with modelCallbacks, but works like this:

Configure::write('Admin.modelLinks', array(
	'Survey.Survey' => array(
		'Download results' => array(
			'url' => array('plugin' => 'survey', 'controller' => 'surveys', 'action' => 'download_results'),
			'options' => array('target' => '_blank')
		), 'Go to survey' => array(
			'url' => array('plugin' => 'survey', 'controller' => 'surveys', 'action' => 'fill'),
			'options' => array('target' => '_blank')
		)
	)
));

![image](https://f.cloud.github.com/assets/218558/1719018/32834622-61e6-11e3-95ec-79e744cc221d.png)