Add param: include_outer_tag

Makes it much easier if you're trying to stick something in the top level of the list:

```
  <ul class="RuledList">
    <li><a href="/{segment_1}/" class="{if segment_2 == ''}is-active{/if}">All Events</a></li>
    {exp:gwcode_categories
      group_id="1"
      show_empty="no"
      include_outer_tag="no"
    }
      <a class="{if '{segment_3}' == '{cat_url_title}'}is-active{/if}" href="/{segment_1}/category/{cat_url_title}/#events">{cat_name}</a>
    {/exp:gwcode_categories}
  </ul>
```