title: Data is not displayed in TableView
body: <p>I try to build simple TableView with model from C++. My table has as many rows and columns, as return rowCount and columnCount method. This means, model is 'connected' with view, but in each cell does not display the message: 'Some data'</p>
  
  <p>here is my code:</p>
  
  <pre><code>class PlaylistModel : public QAbstractTableModel
  {
      Q_OBJECT
  public:
      PlaylistModel(QObject *parent=0): QAbstractTableModel(parent), rows(0){}
  
      int rowCount(const QModelIndex &amp; /*parent*/) const
      {
          return 5;
      }
      int columnCount(const QModelIndex &amp; /*parent*/) const
      {
          return 3;
      }
      QModelIndex index(int row, int column, const QModelIndex &amp;parent) const {
           return createIndex(row, column);
      }
      QModelIndex parent(const QModelIndex &amp;child) const {
           return child.parent();
      }
      QVariant data(const QModelIndex &amp;index, int role) const{
          if (role == Qt::DisplayRole)
               {
                 return QString("Some data");
               }
          return QVariant();
      }
  (...)
  QGuiApplication app(argc, argv);
  QQmlApplicationEngine engine;
  PlaylistModel plModel(0);
  engine.rootContext()-&gt;setContextProperty("myModel", &amp;plModel);
  engine.load(QUrl(QStringLiteral("qrc:///main.qml")));
  </code></pre>
  
  <p>and qml</p>
  
  <pre><code>TableView {
                  id: trackList
                  width: 100; height: 100
                  model: myModel
                  TableViewColumn { role: "id"; title: "Id"; width: 30 }
                  TableViewColumn { role: "name"; title: "Name"; width: 100}
                  TableViewColumn { role: "duration"; title: "Duration"; width: 20 }
  
              }
  </code></pre>
  
  <p>Where I make a mistake?</p>