GtkGradient: Handle symbolic gradients.

GtkGradient: Handle symbolic gradients.

The css parser has been modified to parse correctly radial gradients:

background-image: -gtk-gradient (radial,
                                 center center, 0,
                                 center center, 0.8,
                                 from (#000), to (#fff));

The theming engine has been modified to correctly animate these,
as well as transitions between different pattern types.