CpuWidget using QCharts

Now that the SysInfoWidget base class is ready, let's implement its first child class: CpuWidget. We will now use the Qt Charts API to display a good-looking widget. The average CPU load will be displayed in a pie graph with a hole in the center, like a partly-eaten donut where the eaten part is the percentage of the CPU used. The first step is to add a new C++ class, named CpuWidget, and make it inherit SysInfoWidget:

#include "SysInfoWidget.h" 
 
class CpuWidget : public SysInfoWidget 
{ 
public: 
    explicit CpuWidget(QWidget* parent = 0); 
}; 

In the constructor, the only parameter needed is QWidget* parent. Since we provided default values for the startDelayMs and updateSeriesDelayMs variables in the SysInfoWidget class, we get the best possible behavior; there is no need to remember it when subclassing SysInfoWidget, but it is still...