Feature/formfields

Added possibility to render form fields in columns.
Just define the layout like this:

```
public static $_renderLayout = array(
	'Settings' => array(
		'fullcolumn',
		array('column 1/2', 'column 2/2'),
		array('column 1/3', 'column 2/3', 'column 3/3'),
	),
);
```

I also added a ´double´ form field type.