Override OnDataStorageChanged() to auto select nodes on event

If a data storage is set or reset after SetAutoSelectNewNodes was called
the OnDataStorageChanged() now checks for nodes to auto select, if auto
selection mode is enabled.
Before this change one had to call e.g. SetAutoSelectNewNodes explicitly
after SetDataStorage, if already loaded nodes of an existing data
storage should have been considered when a new node selection widget was
initialized.