We automatically switch the request mode of the container depending on
the GridLayout's orientation, but we need to keep track of the request
mode during allocation, so that we don't get out of sync if the user
changed the request mode after adding the layout manager.
This change also brings us closer to the code in GtkGrid.
We use the orientation of the grid to get the preferred size of the
layout, but we should be using the orientation of the request instead.
The preferred width has an orizontal orientation, and the preferred
height has a vertical orientation.
This allows us to refactor the get_preferred_* implementation into a
separate function.
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
