Use ::keynav-failed for arrow navigation in icon views, so that
it is possible to override error handling. Also add API to get the
row/col of an item. With this, it is possible to make arrow keynav
span adjacent icon views, which is desired in the new control-center
shell. testiconview-keynav demonstrates this.
This commit adds constructors for GtkPaned, GtkBox, GtkButtonBox,
GtkRuler, GtkScale, GtkScrollbar and GtkSeparator and makes these
types instantiable.
* Due to object ownership issues it is impossible to correctly use
get_group/set_group from a GI binding
* join_group is safer because at the binding level it works with individual
GtkRadioAction objects and not with the list of objects that gets
modified in the library
