The ClutterActor API should have modifier methods for adding, removing
and retrieving Actions and Constraints using the ClutterActorMeta:name
property - mostly, for convenience.
To demonstrate that constraints can be used to reposition actors in a
resizable stage, set the :user-resizable property to TRUE, and spend the
next 15 minutes playing with the stage size.
AlignConstraint is a simple constraint that keeps an actor's position
aligned to the width or height of another actor, multiplied by an
alignment factor.
