title: Get keyboard input in my own widget plugin
body: <p>I am making a plugin to CkEditor. It's a widget 
  which is mostly just a h1 with a css class.</p>
  
  <p>That is working fine, but now I need to listen to all keyboard presses when the cursor is in my plugin, because my widget need special actions on some keyboard input.</p>
  
  <p>But how do I listen to keyboard events, when the cursor is in my widget? 
  I can use</p>
  
  <pre><code>editor.on('key', function(event) {
       console.log("Got key up");
  })
  </code></pre>
  
  <p>But then I get all keyboard events in the entire editor. My widget only need/want input if the cursor is within the widget </p>