Fix #1422 Tag select support optgroup

Fix #1422 
```php
$data = array(
	"status",
	array("Active" => array('A1' => 'A One', 'A2' => 'A Two'), "B" => "B One")
);
echo Tag::selectStatic($data);
```
```html
<select id="status" name="status">
	<optgroup label="Active">
	<option value="A1">A One</option>
	<option value="A2">A Two</option>
	</optgroup>
	<option value="B">B One</option>
</select>
```