Initial implementation of the UI definition files. (#424)

	* clutter/json/Makefile.am:
	* clutter/json/*.[ch]: In-tree copy of JSON-GLib, a GLib-based
	JSON parser/generator library. We use it in-tree because we might
	need to change the API. Ideally, we'd depend on it.

	* clutter/clutter.h:
	* clutter/clutter-script-private.h:
	* clutter/clutter-script.[ch]: ClutterScript, the scenegraph
	generator class. It parses JSON streams in form of buffers and
	files and builds the scene.

	* clutter/clutter-debug.h:
	* clutter/clutter-main.c: Add a "script" debug flag

	* clutter/Makefile.am: Build glue.

	* tests/Makefile.am:
	* tests/test-script.c: Add a test case for the ClutterScript.

	* configure.ac: Depend on GLib 2.14, so we can use the
	g_hash_table_get_key() and g_hash_table_get_values() functions
	for the time being; we can probably reimplement those, but we
	are going to need 2.14 anyway if we are going to implement a
	list model using GSequence.