title: Attributes are removed in HTML code
body: <p>I use wysihtml5.
  When you insert an image</p>
  
  <pre><code>&lt;img alt src="src" media_img_id="123" data-title="title" data-author="author" /&gt;
  </code></pre>
  
  <p>The result is</p>
  
  <pre><code>&lt;img alt src="src" /&gt;
  </code></pre>
  
  <p>Rules for img</p>
  
  <pre><code>"img": {
      "remove": 0,
          "check_attributes": {
              "width": "numbers",
              "alt": "alt",
              "src": "url", // if you compiled master manually then change this from 'url' to 'src'
              "height": "numbers",
      "media_img_id": "numbers"
          },
          "add_class": {
              "align": "align_img"
          }
      },
  </code></pre>
  
  <p>How to make the attributes generally not removed?</p>