All the properties now are a GtkCssArrayValue of GtkCssSadowValue. GtkCssArrayValue already does everything we want, so no need to duplicate its funtionality.
Does 3 things: 1) Introduce a "none" array signleton 2) Get rid of memleaks in error paths 3) Reduce code in parse funcs
Make the value auto-cycle its child values, so it can be used for background properties.