[5.14.1] UI adjustments

* OS native check of screen resolution (Qt free, experimental)
* changed rounding
* use string for scale factor so we can use fractions as 2/3
* utility functions to clean numbers, parse fractions

It looks like:

* my WIN10 scaling is 250%
* obviously swift rounds that to 3 (device ratio)
* now using FLOOR policy down-rounding to 2
* rational: scaling up (scale factor) is better as down-scaling as the factors would be clearer
* 2->3 1.5, but 3->2 means 0.66667

src/blackgui/guiutility.h

@@ -66,6 +66,14 @@ namespace BlackGui
         //! \remark might be scaled depending on CGuiUtility::mainApplicationWidgetPixelRatio
         static QSize desktopSize();
 
+        //! Pysical screen resolution
+        //! \remark unscaled
+        static QSizeF physicalScreenSize(QWidget *currentWidget = nullptr);
+
+        //! Qt independent implementation
+        //! \remark allows to return values before QGuiApplication is initialized
+        static QSize physicalScreenSizeOs();
+
         //! Is main window frameless?
         static bool isMainWindowFrameless();