Related #576 High/Low DPI Adapting

The Qt UI would change the size according to the logical DPI of the computer
Only Windows and Linux have been tested. (Should also work on Mac but have not tested).
The function is unfinished.
What about make it a class menber for QWidgetWithDpi and pass it as additional arguments to the QGroupBoxWithDpi and QSpacerItemWithDpi constructors?