* clutter/Makefile.am:
* clutter/clutter.h:
* clutter/clutter-scriptable.[ch]: Add the ClutterScriptable
interface; by implementing this interface, a class can
override the UI definition parsing and transform complex data
types into GObject properties, or allow custom properties.
* clutter/clutter-script.c:
* clutter/clutter-script-parser.c:
* clutter/clutter-script-private.h: Rearrange the code and
use the ClutterScriptable interface to parse and build the
custom properties. This cleans up the code and also it makes
it more reliable (the complex type parsing is now done using
the target type and not just the name of the property).
