title: selectpicker with select all by default
body: <p>I am using the selectpicker <a href="http://silviomoreto.github.io/bootstrap-select/">plugin</a>.
  Now I am trying to select all the options by default, or at least a button to select all without the need of click in the dropdown.</p>
  
  <p>Currently the demo only works if the dropdown is clicked and after that, click the button.</p>
  
  <p>Any idea?</p>
  
  <pre><code>$('.selectpicker').selectpicker();
  
  
  $(".btn_clk").click(function () {
      $('.selectpicker').selectpicker('selectAll');
  });
  </code></pre>
  
  <p><a href="http://jsfiddle.net/tpnw96ed/">http://jsfiddle.net/tpnw96ed/</a></p>