WIP [ticket/12066] Symfony Forms

http://tracker.phpbb.com/browse/PHPBB3-12066

Example Form:

```php
$form = $phpbb_container->get('form')
	->get_builder()
	->setAction(append_sid($phpbb_root_path . 'test.' . $phpEx))
	->add('author', 'text', array(
		'label'  => 'AUTHOR',
	))
	->add('email', 'email', array(
		'label'  => 'EMAIL_ADDRESS',
	))
	->add('number', 'number', array(
		'max_length' => 4
	))
	->add('dueDate', 'date', array(
		'widget' => 'single_text',
		'label'  => 'Due Date',
	))
	->add('submit', 'submit')
	->getForm()
;

$phpbb_container->get('form')->handle_request($form, $request, $symfony_request);

if ($form->isValid())
{
	echo 'valid';
}

$template->set_filenames(array('test' => 'test.html'));

$template->assign_var('testform', $form->createView());

$template->display('test');
```

Template:
```html
{{form(testform)}}
```