added css class to the 'select all' option

i added a css class to the <a> tag of the selected all option.
```html
<li>
<a href="javascript:void(0);" style="padding:0;" class="select-all-option">
<label style="margin:0;padding:3px 20px 3px 20px;height:100%;cursor:pointer;">
   <input style="margin-bottom:5px;" type="checkbox" value="select-all-option">
     Select all
</label>
</a>
</li>
```