Add QImplicitlySharedData to complement QClass

Eventually we'll be able to type:
QClass MyObject
{

slots:
    someSlot();
    //etc
};

To complement that, we should have QImplicitlySharedData (or something with a shorter name). ex:
QImplicitlySharedData Employee
{
    int id;
    QString name;
};

In case it isn't obvious, that then generates the stuff necessary for Implicit Sharing as seen here: http://doc.qt.io/qt-5/qshareddatapointer.html#details