title: get selector of specific div in jsplumb
body: <p>I created a div and I want to make it draggable using: </p>
  
  <pre><code>mydiv_selector = jsplumb.getSelector('.classname');
  JSPLUMB_INSTANCE.draggable(mydiv);
  </code></pre>
  
  <p>how do I get the "selector" of a specific div? (instead of getting the selector of all divs in that classname) jsplumb.getSelector() seems to take a classname, but I have many elements in that class. Can I get the specific div by ID or something else?</p>