title: with draft.js is it possible to create a custom block span with classname
body: <p>I am using draft.js, and I have everything I need working except for one thing.  </p>
  
  <p>I want to be able to add a custom block option that will apply a span with a custom class (e.g. content) around the selected content in the editor.</p>
  
  <p>Is this possible with draft-js custom blocks?</p>
  
  <p>Any good examples out there? (didn't find anything when googling)</p>