Fixing PHPDoc’s to support object array auto-complete in IDE

I've updated several PHPDoc's to allow IDE's auto-complete for methods, that returns array of objects, like `findAll`.

Code example to enable auto-complete before this PR:
```php
/** @var NodeElement $element */
foreach($page->findAll('css', 'input') as $element) {
// ...
}
```

After this PR no extra `@var` comment is needed to enable auto-complete in IDE.