Implement Ordering like in Zend Navigation

add option `order` to enable ordering for that page item
`-1` means always first (if two or more elements have -1 one will win)
no order option will just behave as before

Example:
```
array(
    array(
        'options' => array(
            'uri' => 'http://www.child1.com',
            'name' => 'child1',
	    'order' => 100,
        ),
        'attributes' => array(
            'class' => 'child1-class',
        ),
    ),
    array(
        'options' => array(
            'uri' => 'http://www.child1.com',
            'name' => 'child1',
        ),
        'attributes' => array(
            'class' => 'child1-2-class',
        ),
    ),
    array(
        'options' => array(
            'uri' => 'http://www.child2.com',
            'foo' => 'bar',
            'name' => 'child2',
	    'order' => -1,
        ),
        'attributes' => array(
            'class' => 'child2-class',
        )
    ),
    array(
        'options' => array(
            'uri' => 'http://www.child3.com',
            'foo' => 'bar',
            'name' => 'child3',
        ),
        'attributes' => array(
            'class' => 'child3-class',
        )
    )
);

```