[ticket/12838] Add ACP events to acp_ranks

https://tracker.phpbb.com/browse/PHPBB3-12838
I'd prefer something like:
```php
	if ($row['rank_special'])
	{
		unset($row['rank_min']);
		$ranks['special'][$row['rank_id']] = $row;
	}
	else
	{
		$ranks['normal'][$row['rank_id']] = $row;
	}
```