Add signal emission methods to TreeModel which coerce the path argument

Override TreeModel row_changed, row_inserted, row_has_child_toggled,
row_deleted, and rows_reordered methods to accept python iterables as
the path parameter. This is for compatibility with pygtk and consistency
with the rest of the TreeModel and TreePath overrides.

https://bugzilla.gnome.org/show_bug.cgi?id=682933