* Normalized 'change-region' so (almost) all commands are context sensitive (use 'root' or '..' to set 'all scenes' context)
* 'terrain-sim' is thusly obsolete, use 'change-region', followed by 'terrain'
* Introduced SceneManager to administrate operations on group of scenes and moved relevant funcs there.
* In it, there's a ForEach(Action<Scene>) that either passes all scenes, or only current scene depending on context.
* Changed default prim backup (save-xml/load-xml) xml to "prim-backup.xml"
* Changed Disable/EnablePermissions to BypassPermissions = true/false;
Also:
* Removed unused and non-existent project ref
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