Rename StructureList and AbstractStructure

Rename StructureList to DynamicNode and AbstractStructure to StaticNode.
The idea is that "dynamic" can have its length changed, while "static"
doesn't. I don't think this is the best names for those structures, but
they are definitely better than the originals.
Add a few more todos
Fix rendering of function calls as statements

I don't like to override render on language specific nodes, but I don't
see another way at the moment.