title: Colspan and Rowspan in CellTable
body: <p>I'm implementing a table which has both colspan and rowspan cells. I used FlexTable before but decided to use CellTable. But it looks like CellTable does not support adding style while FlexTable did... Please look at the picture to know what I'm trying to do:</p>
  
  <p><img src="https://i.stack.imgur.com/RDPvx.png" alt=""></p>
  
  <p>Any suggestions are welcome.</p>