refactored Limaki.Drawing.ISystemColors => Xwt.SystemColors / Xwt.Backends.SystemColorsBackend
SceneTestEnvironment: introduced ReportScene to write a Html5 (as Xwt.Toolkit.Guest) drawing the Scene
renames proove => prove
GCJohnBostonSceneTest: refactored to have EdgeExpand-Tests out of Person-Test | PersonJohnGoEdge uses  ReportScene
GraphSceneFacade: Expand walk optimized  to call ToArray only once