refs #335, style sheet fixes / improvements and support methods

style sheets:
* style sheets with background textures
* scroll area / toolbox style sheet fix
* floating dock widgets
* kept 1st version of stylesheets in backup directory
* removed maininfoarea stylesheet, no longer needed with fixed style sheet

code
* central paintEvent method to enable style sheets in derived widgets
* detect frameless windows, dynamic properties

src/blackgui/guiutility.h

@@ -26,6 +26,9 @@ namespace BlackGui
         //! Main application window
         static QMainWindow *mainWindow();
 
+        //! Is main window frameless?
+        static bool isMainWindowFrameless();
+
         //! Top level widgets with names
         static QWidgetList topLevelApplicationWidgetsWithName();