Abstract class for event-related logic
<clutter-action> is an abstract base class for event-related
actions that modify the user interaction of a <clutter-actor>,
just like <clutter-constraint> is an abstract class for modifiers
of an actor's position or size.
Implementations of <clutter-action> are associated to an actor
and can provide behavioral changes when dealing with user input - for
instance drag and drop capabilities, or scrolling, or panning - by using
the various event-related signals provided by <clutter-actor>
itself.
<clutter-action> is available since Clutter 1.4