title: Adding an "all" option on categories
body: <p>This may seem like a basic question but I hope somebody could help me out. </p>
  
  <p>I have a created a widget for a custom post type so that I could show the post types in a dynamic sidebar. In the widget, I have also created a dropdown that gets the categories to show. </p>
  
  <p>My problem is that I also want to have the option to show all the categories and not just 1 category for the dropdown. Here's the code I have so far:</p>
  
  <pre><code>    &lt;select id="&lt;?php echo $this-&gt;get_field_id('articleCategory'); ?&gt;"  name="&lt;?php echo $this-&gt;get_field_name('articleCategory'); ?&gt;"&gt;
      &lt;?php $arr = get_categories(); ?&gt;
      &lt;?php foreach($arr as $option) { ?&gt;
      &lt;option &lt;?php echo $instance['articleCategory'] == $option-&gt;term_id ? 'selected="selected"' : '';?&gt; value="&lt;?php echo $option-&gt;term_id; ?&gt;"&gt;&lt;?php echo $option-&gt;name; ?&gt;&lt;/option&gt;
      &lt;?php } ?&gt;
      &lt;/select&gt;
  </code></pre>
  
  <p>Should I just use a multi-select for this and how do i go about it? </p>