layout-manager: Deprecate the layout animation

layout-manager: Deprecate the layout animation

This semi-aborted API was broken for various reasons:

  - it strongly depended on ClutterAlpha, a class we're trying to
    deprecate;
  - it requires a lot of boilerplate and copy-and-paste code;
  - it requires a full relayout of the actor tree for something
    that ought to be automatically handled by ClutterActor.

Now that clutter_actor_allocate() handles transitions using the easing
state of the actor, we can deprecate the LayoutManager API for the 1.x
series, and remove it for the 2.x series.