refs #485, moved central GUI functionality to sGui

* allow to send status message to main window (from everywhere)
* Use sGui::changedStylesheet where possible
* message when model is stashed
* improved application startup

src/blackgui/guiutility.cpp

@@ -42,7 +42,7 @@ namespace BlackGui
         return nullptr;
     }
 
-    QWidget *CGuiUtility::mainApplicationWindowWidget()
+    QWidget *CGuiUtility::mainApplicationWindow()
     {
         CEnableForFramelessWindow *mw = mainFramelessEnabledApplicationWindow();
         if (mw && mw->getWidget())