Fix #1422 Tag select support optgroup

[dreamsxin]

Fix #1422

$data = array(
    "status",
    array("Active" => array('A1' => 'A One', 'A2' => 'A Two'), "B" => "B One")
);
echo Tag::selectStatic($data);

<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>