title: Custom button in toolbar draftjs editor
body: <p>How can I add a button with a custom function behind it to the draftjs editor? I have the feeling this should be pretty straightforward but I can't find examples or documentation.</p>
  <p>I have an Editor with only bold italic and list buttons and I want to add a button that shows a popup where I can select 1 of 3 options and then &quot;inject&quot; this in the editor.</p>
  <p>Can someone point me in the right direction (or documentation)?</p>