Do not use the text() of the Action to show a DockWidget

The text can be translated, the text can have accelerator-special
key, so the text is unrealiable. the only thing reliable is the data,
wich stores a pointer to a fixed , unmutable, string.
Signed-off-by: Tomaz Canabrava <tomaz.canabrava@intel.com>

src/ui/MainWindow.cc

@@ -402,7 +402,7 @@ void MainWindow::_showDockWidgetAction(bool show)
 {
     QAction* action = qobject_cast<QAction*>(QObject::sender());
     Q_ASSERT(action);
-    _showDockWidget(action->text(), show);
+    _showDockWidget(action->data().toString(), show);
 }
 #endif