with correct form input input prepend / append is on wrong div

class should not be on control-group

e.g.

```html
<script type="text/javascript">
    $(document).ready(function() {
        $('#div_id_til').datetimepicker({
            format: 'yyyy-MM-dd hh:mm',
            language: 'nb-NO'
        });
    });
</script>
```
This breaks the layout:

```html
<div id="div_id_til" class="control-group input-append">
    <label for="id_til" class="control-label required-field">Til</label>
    <div class="controls">
            <input name="til" type="text" id="id_til" value="2013-04-10 23:59" />
            <span class="add-on">
                <i data-time-icon="icon-time" data-date-icon="icon-calendar"></i>
            </span>
            <p class="help-block">Når arrangementet slutter</p>
    </div>
</div>
```
This breaks the js:

```html
<div id="div_id_til" class="control-group">
    <label for="id_til" class="control-label required-field">Til</label>
    <div class="controls">
        <div class="input-append">
            <input name="til" type="text" id="id_til" value="2013-04-10 23:59" />
            <span class="add-on">
                <i data-time-icon="icon-time" data-date-icon="icon-calendar"></i>
            </span>
            <p class="help-block">Når arrangementet slutter</p>
        </div>
    </div>
</div>
```

This pull fixes the problem with the js