It's time. Now that we have clutter_actor_allocate() respecting the
easing state of an actor, and that the LayoutManager animation virtual
functions have been deprecated, we can put ClutterAlpha on the chopping
block, and be done with it, once and for all.
So long, ClutterAlpha; and thanks for all the fish.
This moves a couple of definitions to the common types header, and makes
sure that ClutterBehaviour subclasses include clutter-behaviour.h first,
so that their types can be fully expanded without necessarily have the
ClutterBehaviour header header included by their public headers. This is
the necessary prelude to have clutter-behaviour.[ch] moved to the
deprecated section.
