Added Option to add wraper to input field and class for lable

I have worked in this to add a wrapper to only input field by using the below keys

```PHP
$f->add_input('Im a little field', array('class'=>array('form-control'),
                                             'wrap_tag' => 'div',
                                             'wrap_class' => 'form-group',
                                             'input_wrap_tag' => 'div',
                                             'input_wrap_class' => 'col-md-4',
                                             'input_wrap_id' => 'span'  ), 'little_field');
```

and also added an option to add class for lable
```PHP
 $f->add_input('Im a little field', array('class'=>array('form-control'),
                                             'lable_class' => 'col-md-4', ), 'little_field');
```