Checkboxes and radios don't show in form

In the Form.php example you don't have 'checkbox' as an available type and the 'radio' type is actually named 'filter_radio'.

So it needs

```
private $types = array(
  'text'=>1,
  'p'=>1,
  'select'=>1,
  'textarea'=>1,
  'filter_radio'=>1,
  'checkbox'=>1,
);
```

And `function build_radio($id,$data)` needs to be changed to `function build_filter_radio($id,$data)`.
