engine interaction class refactoring, round 4 or 5, can't remember: this time use the class methods to create an instance object and operates on that, reducing the number of arguments between methods and simplifying memory management

#include <QtGui/QApplication>
#include "mainwindow.h"

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();
    return a.exec();
}