6353: Fix error when setting colours

git-svn-id: svn+ssh://svn.code.sf.net/p/gramps/code/trunk@21163 4ae1f11a-8b86-4847-b8af-ab372f36d1fd
Use public interface of Gtk.TreeModel in listview code

git-svn-id: svn+ssh://svn.code.sf.net/p/gramps/code/trunk@21165 4ae1f11a-8b86-4847-b8af-ab372f36d1fd