Fix flickering in the project pane.

This isn't a nice fix but the least evil version of a hack i could come
up. The source of the flickering is: We have a deeply nested structure
of widgets on the project pane. If we call hide() on such a deeply
nested widget, it will activate() it's parent layout synchronously.
That will then post an event (via updateGeometries() ) to its parent
layout that it needs relayouting. Which then will post to its parent
layout the same. And for each LayoutRequested, there's a painting in
between. The fix instead calls activate() up the chain until we are at
the viewport. This immediately relayouts everything. This adds a non
obvoius potentially for breakeage if the widgets are embedded in a
different widget hierarchy. But well, that's life.

src/plugins/projectexplorer/projectwindow.cpp

@@ -76,8 +76,9 @@ PanelsWidget::PanelsWidget(QWidget *parent)
     topwidgetLayout->addWidget(verticalWidget);
     topwidgetLayout->addStretch(10);
 
-    setWidgetResizable(true);
     setFrameStyle(QFrame::NoFrame);
+    setWidgetResizable(true);
+
     setWidget(topwidget);
 }