title: Django: django-tables2 Changing default sort behaviour
body: <p>I'm experimenting with django-tables2. I've created a test site that displays a column of dates (created by <code>timezone.now()</code>). By default, the dates are ordered Oldest->Newest. If I click on column header, the dates are displayed in reverse order (the desired default behavior).</p>
  
  <p>I've played around with the <code>order_by</code> argument, but I'm doing something wrong. My tables.py:</p>
  
  <pre><code>class OrderTable(tables.Table):
      order_date = tables.Column(order_by=("Order Date",))
  </code></pre>
  
  <p>My views.py:</p>
  
  <pre><code>def index(request):
      table = OrderTable(Order.objects.all())
      RequestConfig(request, paginate={"per_page": 10}).configure(table)
      return render(request, 'orders_app/index.html', {'table': table})
  </code></pre>
  
  <p>How can I order the "Order Date" column so its displayed as Newest->Oldest?</p>