Generates:
<div class="panel-grid">

   <div class="panel-grid-cell">
        <div class="panel">
         Column 1
        </div>
   </div>

   <div class="panel-grid-cell">
        <div class="panel">
         Column 2
        </div>

        <div class="panel">
         Column 3
        </div>
   </div>
</div>