GListModel support

GtkFilterListModel — A list model that filters its items
GtkFlattenListModel — A list model that flattens a list of lists
GtkMapListModel — A list model that transforms its items
GtkSliceListModel — A list model that presents a slice out of a larger list
GtkSortListModel — A list model that sorts its items
GtkTreeListModel — A list model that can create child models on demand
GtkSelectionModel — An extension of the list model interface that handles selections
GtkSingleSelection — A selection model that allows selecting a single item