Remove SecondPage.qml
ClusterList: Remove inheritance of QAbstractListModel, and make ClusterNode inherit QObject.
ClusterNode: Define internalId and title as Q_PROPERTY.
Cluster.cpp, Main: Remove debug-related line.
Merge branch 'clusterlist_without_QAbstractListModel'
ClusterList: Add titles() and titlesModel() properties, which provide lists / listmodels for the ClusterNodes in a ClusterList.
ClusterNode, ClusterList: add default argument to constructors.
ClusterList: Change the return type of the titlesModel, from QStringListModel to QStringListModel*.
FirstPage: Remove default code and add basic SilicaListView on the page.
ClusterNode: Remove dependency on QObject. ClusterNode is now a simple class with two pure virtual methods.
ClusterList: Remove the Q_OBJECT macro and the defined Q_PROPERTY.
ClusterList: Remove methods titles() and titlesModel(), as they will be replaced with implementations of QAbstractListModel functions.
ClusterList: Define ClusterList as derivative of QAbstractListModel, and provide implementations for the required virtual methods.
Remove dependency of ClusterNode on QObject, and rebase ClusterList on QAbstractListModel.
ClusterList: Remove "explicit" qualifier from the constructor. It's completely unnecessary.
ClusterList: For learning purposes, differentiate between Data Roles in the data() method.