title: PyQt: Creating a table with multiple header
body: <p>I have created an application for my work which takes data from a database, does some calculations with it and dumps it into a table for viewing. Easy peasy. But, there has been a request to change the way information is shown. Previously it was using a simple tablewidget and a very standard table.
  My problem arises with the headers mostly.
  This is an idea of what I've been asked to change the layout to:
  <img src="https://i.stack.imgur.com/1oNza.png" alt="enter image description here"></p>
  
  <p>As you can see, there is a top header with columnspan over the second header which in turn has it about the third. The third header (with little numbers) is not essential but the other two headers are. For what it's worth, under the months the calculated numbers will be displayed. 
  My question is, how would I be able to create a table to make such a layout? </p>