title: Load options on the first open of the Async drop down menu
body: <p>When I provide <code>loadOptions</code> to an <code>Async</code> control it loads options on mount.</p>
  
  <p>If I pass <code>autoload={false}</code> then it doesn't load options neither on mount nor on open. But it loads options on the first close (or type, or blur).</p>
  
  <p>If I pass <code>onCloseResetsInput={false}</code> then it doesn't load options until I type something. (showing "Type to search" in the menu)</p>
  
  <p><code>Async</code> provides <code>onOpen</code> handler, but I didn't find the way to use it in this situation. (and <code>react-select@2.0.0-alpha.2</code> doesn't have it)</p>
  
  <p>So the user needs to type a character, then delete it, to see the full list of options.</p>
  
  <p>How can this be avoided?</p>
  
  <p><strong>Example sandbox</strong>: <a href="https://codesandbox.io/s/mjkmowr91j" rel="noreferrer">https://codesandbox.io/s/mjkmowr91j</a></p>