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
The basic MetaShadowFactory type is moved to a public header, while
the functions to fetch and paint shadows are kept private.
The public object will be used for configuration of shadows by
plugins.
https://bugzilla.gnome.org/show_bug.cgi?id=592382