Actor: Add most missing methods.

* clutter/src/actor.[hg|ccg]: Added get_paint_box(),
  set_child_below/above_sibling(), set_child_at_index(),
  has_key_focus(), get_paint_volume(), get_transformed_paint_volume(),
  get_default_paint_volume(), get_children(), get_n_children(),
  get_child_at_index(), get_previous/next_sibling(),
  get_first/last_child(), allocate_align_fill(),
  get_child_transform(), detach_animation(),
  get_actions(), has_actions(), get_effects()
  and has_effects().
* codegen/m4/convert_clutter.m4: Add a conversion for PaintVolume.