Create a Playset or Setting object that can specify a custom tree of existing objects for use in a specific setting (independant of the RulesPackage)

[rsek]

Use cases:

• Integrating the sundered isles tree with starforged (one for each of SI's "realms")
• user-created trees that describe a specific setting and/or integrate 3rd party content

[cwegrzyn]

@rsek Were you roughly thinking that this would be a list of IDs / ID patterns? We are bumping against the immediate use case of "which truths do we show you?" when Starforged and SI are enabled, and it would be nice to solve this in a way that ultimately lets us roughly swap in the official solution with minimal change!