title: How to add add a custom attribute for each input field in Sitecore Webforms for Marketer
body: <p>I am using Sitecore 8.1 with WFFM for marketer.
  I have to add one additional input attribute called "custom_attr" in each field of webform ( textbox,radiobtn,checkbox,dropdown) and editor can add some text inside it and it will render in UI .</p>
  
  <p>How to add a custom input attribute that display when html get render in Sitecore Webform for marketer in MVC i.e.</p>
  
  <pre><code>&lt;input type='text' custom_attr='some_msg'/&gt;
  &lt;select custom_attr='some_msg'&gt;&lt;option&gt;&lt;/option&gt;&lt;select&gt;
  &lt;input type='chekbox' custom_attr='some_msg'/&gt;
  &lt;input type='radio' custom_attr='some_msg'/&gt;
  </code></pre>
  
  <p>Is there we have a global way to add this attribute in one place and it render for all fields ? </p>