title: Custom columns using Django admin
body: <p>I have a model <code>Data</code>, associated to a table like this (The model <code>Data</code> is made up of only IntegerField):</p>
  
  <pre><code>subject | year | quarter | sales |
  ----------------------------------
     1    | 2010 |   1     | 20    |
     1    | 2010 |   2     | 100   |
     1    | 2010 |   3     | 100   |
     1    | 2010 |   4     | 20    |
     1    | 2011 |   1     | 30    |
     1    | 2011 |   2     | 50    |
     1    | 2011 |   4     | 40    |
     2    | 2010 |   1     | 30    |
     2    | 2010 |   2     | 20    |
   [..-GO ON this way...]
  </code></pre>
  
  <p>I want to have a django-admin table, in read-only having columns (<code>current year = 2011, quarter = 1</code>)</p>
  
  <pre><code>subject | sales current year | sales current quarter | sales last year | sales current quarter last year |
  ----------------------------------------------------------------------------------------------------------
    1     |  110               |  30                   |  240            |  20
  [AND SO ON]
  </code></pre>
  
  <p>The question is: <strong>It is possible do that using django-admin? What's the way out?</strong></p>