Use south tabs in the debugger

The current northpointing dockwidget layout looks
broken since we repeat the label when the docks are
unlocked. We also dont line up properly with the header sections.
Other dock widgets in designer are also using the south tab so
this would be more consistent.

Reviewed-by: danimo

src/plugins/debugger/debuggeruiswitcher.cpp

@@ -326,7 +326,6 @@ Utils::FancyMainWindow *DebuggerUISwitcher::mainWindow() const
 QWidget *DebuggerUISwitcher::createMainWindow(Core::BaseMode *mode)
 {
     d->m_mainWindow = new DebuggerMainWindow(this);
-    d->m_mainWindow->setTabPosition(Qt::AllDockWidgetAreas, QTabWidget::North);
     d->m_mainWindow->setDocumentMode(true);
     connect(d->m_mainWindow, SIGNAL(resetLayout()),
             this, SLOT(resetDebuggerLayout()));