PieceUnit and PieceUnitFactory created

I created these two classes. The first is an instance of the qml representation and the second a factory class as the name suggests. The code doesn't compile though... It's complaining in the constructor of the factory, so I must be doing something wrong there. Don't merge the changes if some button suggests so. This is meant mostly to help me understand how the constructor initialization works, and spot all the mistakes that I've done so far