Instead of setting shadow parameters on individual windows, add the
idea of a "shadow class". Windows have default shadow classes based
on their frame and window type, which can be overriden by setting
the shadow-class property.

Each shadow class has separably configurable parameters for the
focused and unfocused state. New shadow classes can be defined with
arbitrary names.

https://bugzilla.gnome.org/show_bug.cgi?id=592382