implemented workaround for QPainter to render widget ontop of opengl.

problem was mainly observed on osx

SelectionBasePlugin.cc

@@ -221,6 +221,8 @@ void SelectionBasePlugin::initializePlugin() {
     pickModeToolBar_->addSeparator();
     pickModeToolBar_->addActions(selectionModesGroup_->actions());
 
+    pickModeToolBar_->setWindowOpacity(0.99);
+
     emit setPickModeToolbar(SELECTION_PICKING, pickModeToolBar_);
 }