Add Define Class wizard specialization for QAbstractItemModel

It would be nice if there were a few more choices in this wizard. Creating a QAIM subclass is complex enough that I always have to read docs again to remind myself which virtual functions I need to override. The wizard should be able to help me decide whether to subclass QAIM itself (for tree models or for ultimate flexibility), QAbstractListModel or QAbstractTableModel. I'd like to have checkboxes for whether the model should have a tree structure or not; whether it should be editable or not; and whether it should have a roles enum, multiple columns, or both. Perhaps there should be a way to add specific role/column names on a separate wizard page. If both roles and columns are enabled, the result should be a universal model that can be used with QListView, QTableView (widgets), ListView and TableView (Qt Quick) as explained in https://youtu.be/-GOfY1kEP2A and https://youtu.be/moWNU-WJCVY