[Gtk] cleanup tree backend code
[Gtk] implement ITreeDataSource events
Merge branch 'gtk-tree-fixes' into add-tree-filter
[Gtk] move ITreeDataSource impl. to new TreeStoreBackendBase
[Gtk] add TreeStoreFilterBackend implementation
[Gtk] move IListDataSource impl. to new ListStoreBackendBase
[Gtk] add ListStoreFilterBackend implementation
[Gtk] support TreeStoreBackendBase as native store
backend for TreeViewBackend
[Gtk] support ListStoreBackendBase as native store
backend for ListViewBackend
[Gtk] fix store model access in *StoreBackendBase classes
[Mac] register default tree/list store and filter backends
Add Tree/List filter examples