ForceObjects parameter for SceneCache ROP

Users requested a way to control what is written as links and what is expanded. This has been implemented using a node list filter, since that is a common concept in ROPs (matches Mantra behaviour). This allows users to force specific objects to expand (and force the unlisted objects to be links, if possible). An empty value will behave as normal (no forced behaviour) and the parameter is disabled when writing normal .scc files.