Fixes Node _call and _callStatic to be usable

<h3>Summary</h3>
I assume the intetion of introducing (14a748c363d428244db79f2516d6e6f540d40202) these magic methods along with `Node::registerMethod()` was providing end user to use code like:

```php
/* page part / snippet / layout code */
$this->doSomethingCoolWithThisPage('very cool');
```

This would call appropriate method registered with a plugin and this way greatly simplify and extend `$this` (Page) usage in page parts / layouts / snippets by providing plugin-provided `$this` scope methods.  

<h4>Problem</h4>

The problem with current implementation was misuse of `call_user_func` in `__call` and `__callStatic` which should be replaced with  `call_user_func_array` to pass array of parameters into registered method.

Moreover `array_unshift` operates on array reference and ***returns count of array elements*** after addition instead of the ***actual array*** of method parameters prepended by object. This virtually passed an useless integer to callable function.

<h4>Solution</h4>
 
See the **diff** for proposed code, and below I provide drop-in addition to ***skeleton/index.php*** for the purpose of testing the code. IMO it works as expected now.

```php
<?php
/*
 * Exposes usage of instanceTest($type)
 * in page part/layout/snippet
 * 
 * example:
 * $this->instanceTest('h3');
 * 
 * should echo page title wrapped in H3 html tags
 */
Page::registerMethod('instanceTest', 'skeleton_instance_test');
function skeleton_instance_test($that, $type) {
    echo '<' . $type . '>' . $that->title() . '</' . $type . '>';
}

/*
 * Exposes usage of class level method
 * in page part/layout/snippet
 * 
 * example:
 * Page::staticTest(4);
 * 
 * should echo page (id=4) object wrapped in PRE html tags
 */
Page::registerMethod('staticTest', 'skeleton_static_test');
function skeleton_static_test($that, $id) {
    echo '<pre>';
    if ($page = $that::findById($id)) {
        echo html_encode(print_r($page));
    } else {
        echo 'Page with id ' . $id . ' not found!';
    }
    echo '</pre>';
}
```

To test this, just enable modified **skeleton** and put the code below into a page part

```php
<?php
$this->instanceTest('H3');
$this->instanceTest('H2');
$this->instanceTest('PRE');
Page::staticTest(4);
Page::staticTest(1234);
?>
```