MultipleInheritance: Improve code and documentation

Task-number: QTBUG-61419
Change-Id: I858027db3ca83a4fe41a576919acbb408db35cff
GPush-Base: 8abb03b0d84a3a94f7db41e010f69955488ea893
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>

examples/uitools/multipleinheritance/calculatorform.cpp

 /****************************************************************************
 **
-** Copyright (C) 2016 The Qt Company Ltd.
+** Copyright (C) 2017 The Qt Company Ltd.
 ** Contact: https://www.qt.io/licensing/
 **
 ** This file is part of the examples of the Qt Toolkit.
@@ -48,8 +48,8 @@
 **
 ****************************************************************************/
 
-#include <QtWidgets>
 #include "calculatorform.h"
+#include <QWidget>
 
 
 //! [0]

examples/uitools/multipleinheritance/calculatorform.h

 /****************************************************************************
 **
-** Copyright (C) 2016 The Qt Company Ltd.
+** Copyright (C) 2017 The Qt Company Ltd.
 ** Contact: https://www.qt.io/licensing/
 **
 ** This file is part of the examples of the Qt Toolkit.
@@ -61,7 +61,7 @@ class CalculatorForm : public QWidget, private Ui::CalculatorForm
     Q_OBJECT
 
 public:
-    CalculatorForm(QWidget *parent = 0);
+    explicit CalculatorForm(QWidget *parent = nullptr);
 
 private slots:
     void on_inputSpinBox1_valueChanged(int value);

examples/uitools/multipleinheritance/main.cpp

@@ -48,8 +48,8 @@
 **
 ****************************************************************************/
 
-#include <QApplication>
 #include "calculatorform.h"
+#include <QApplication>
 
 //! [0]
 int main(int argc, char *argv[])

examples/uitools/multipleinheritance/multipleinheritance.pro

 #! [0]
-SOURCES = calculatorform.cpp main.cpp
+QT += widgets
+
 HEADERS = calculatorform.h
+SOURCES = calculatorform.cpp main.cpp
 FORMS = calculatorform.ui
 #! [0]
 
 target.path = $$[QT_INSTALL_EXAMPLES]/uitools/multipleinheritance
 INSTALLS += target
 
-QT += widgets