title: QTableView filtering with QSortFilterProxyModel (grouping filters)
body: <p>It seems I am not capable of filtering more then one column at once. I think it's common usage when using filters, maybe I'm missing something.</p>
  
  <p>For example, i have 4 columns in my <code>QTableView</code>, let's say column <code>X (string), Y (int), Z (string), Q (string)</code>. I wish to filter by <code>filter_1</code> column <code>X</code> and filter by <code>filter_2</code> column <code>Z</code>. Is it possible to set <code>QSortFilterProxyModel</code> filter for more then one column (dynamically), but not all (re implementing <code>filterAcceptsRow</code>).</p>
  
  <p>Thanks</p>