title: Edit default element in visual composer - single image - to be able to add alt tag
body: <p>Hi I am trying to edit the visual composer plugin, specifically a default element "single image".</p>
  
  <p>I want to be able to add a section where I can add a alt tag to the image - because I use some images more than once on different pages using the standard wordpress alt tags means I would need to upload the image multiple times.</p>
  
  <p>I have used visual composer on other sites that has been customized by the theme author and it has this function already but I can't seem to get it to work on the standard visual composer.</p>
  
  <p>I added this code into the PHP file:</p>
  
  <pre><code>    array(
      'type' =&gt; 'textfield',
      'heading' =&gt; __( 'Image ALT tag', 'js_composer' ),
      'param_name' =&gt; 'image_alt',
      'holder' =&gt; 'alt',
      'description' =&gt; __( 'Enter the image alt text.', 'js_composer' ),
  </code></pre>
  
  <p>And it worked as far as adding the alt tag text box but this didn't translate to the front end where it was still pulling the alt tag from the title tag added in the media library.</p>
  
  <p>Am I missing a function or something here?
  </p>