title: Boostrap multiselect select all checked by default
body: <p>i use bootstrap-multiselect (v0.9.8) with option</p>
  
  <pre><code> includeSelectAllOption: true 
  </code></pre>
  
  <p>it is posible that select all to be checked by default when page is loaded?</p>
  
  <p>thx.</p>