title: Visualization: Grouped and stacked Bar chart
body: <p>I've got the following pands dataframe:</p>
  
  <pre><code>date    allocated_reason        allocated   bk_task
  
  2019-10-27  AI               Allocated  1051
  2019-11-03  AI               Allocated  1471
  2019-10-27  Self Allocation      Allocated  291
  2019-11-03  Self Allocation      Allocated  274
  2019-11-10  Self Allocation      Allocated  40
  2019-10-27  AI               Not Allocated  3570
  2019-11-03  AI               Not Allocated  3267
  2019-11-10  AI               Not Allocated  598
  </code></pre>
  
  <p>The date is the index and bk_tasks is the number of tasks for each combination: 
  E.g. 1051 tasks in the week of 27/10 who are AI + Allocated.</p>
  
  <p>I want to make a bar-plot witch has 2 bars for each week: 1 bar contains the number of not allocated tasks, the other the allocated task, and I want each bar to be grouped by AI or Self Allocation. </p>