ClutterGridLayout is port of GtkGrid to a Clutter layout manager. All
the logic is taken from gtkgrid.c, so all the credits should go to
Matthias Clasen for writing this nice piece of code.
ClutterGridLayout supports adding children with it's own methods
GridLayout.attach() and GridLayout.attach_next_to() as well as
Actor.add_child() and friends. The latter adds children in a similar
fashion to ClutterBoxLayout
https://bugzilla.gnome.org/show_bug.cgi?id=677372
