Use a hash QHash<QTreeWidgetItem*,Pages*> instead of QHash<int,Pages*> m_pagehash

This way, the integer stored in QT::UserRole is not needed at all.  The hash
directly allows for conversion from a known treeWidgetItem to a page.  Since
the integer is not required to be passed and held in subclasses of the pages
class, clean up the constructors of Subclasses to not get the integer value
and set back to nearly like they were before.