* demos/gtk-demo/example_dropdown.cc: Use some lambda expressions.
* demos/gtk-demo/example_listview_columnview.cc:
* demos/gtk-demo/example_listview_editable_cells.cc:
* demos/gtk-demo/example_listview_liststore.cc:
* demos/gtk-demo/example_listview_treelist.cc: Add add_css_class("data-table").