title: How to add checkall and uncheck all option for jquery multiselect?
body: <p>I have added jquery multiselect property for my dropdown. Dropdown is like this,</p>
  
  <pre><code>&lt;div&gt;
  &lt;select id="selectChartType" multiple="multiple" size="5" style="width:25px" &gt;
        &lt;option value="option1"&gt;option1&lt;/option&gt;
        &lt;option value="option2"&gt;option2&lt;/option&gt;
        &lt;option value="option3"&gt;option3&lt;/option&gt;
        &lt;option value="option4"&gt;option4&lt;/option&gt;
        &lt;option value="option5"&gt;option5&lt;/option&gt;
        &lt;option value="option6"&gt;option6&lt;/option&gt;
        &lt;option value="option7"&gt;option7&lt;/option&gt;
        &lt;option value="option8"&gt;option8&lt;/option&gt;
        &lt;option value="option9"&gt;option9&lt;/option&gt;
        &lt;option value="option10"&gt;option10&lt;/option&gt;
  &lt;/select&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>I am initializing multiselect like this,</p>
  
  <pre><code>$(document).ready(function() {
       $("#selectChartType").multiselect({
       header:false,
       noneSelectedText:"options",
       minWidth: 190
        });
  });
  </code></pre>
  
  <p>I want 2 options inside the dropdown saying checkall and uncheckall. I know there is a option,</p>
  
  <pre><code>$("#selectChartType").multiselect({CheckAll});
  </code></pre>
  
  <p>But i don't know how to add it in html. Please help me</p>