Simplify some name handling in the graph structures. Pass the host object into the decoration
Fix an initialization problem with the Decoration base class
Fix small bug in the use of the class name for node types in the graph data structure
This is a really big commit that should have been split into a lot
of small ones. It moves all location information and layout into
a single graph class, LayoutInfo. All of the builder functions
have been unified in LayoutBuilder.