title: Polymer: Detect click outside of custom element
body: <p>I have a custom element and would like to detect clicks outside of it. For example</p>
  
  <pre><code>&lt;dom-module id="simple-element"&gt;
  
  
  
  &lt;style&gt;
    &lt;/style&gt;
  
    &lt;template&gt;
      &lt;content&gt;&lt;/content&gt;
    &lt;/template&gt;
  
  &lt;/dom-module&gt;
  
  &lt;script&gt;
    (function() {
      Polymer({
        is: 'simple-element',
        listeners: {
          'tap': 'regularTap'
        },
        regularTap: function() {
          console.log("i was tapped");
        }
      });
    })();
  &lt;/script&gt;
  </code></pre>
  
  <p>Is there an event where I can listen to which will tell me when user has clicked outside of the element? Thanks.</p>