Split octree file format in some way to allow for better error handling

Currently if anything in octree loading has any error the state of everything is unknown, and any data that hasn't yet been loaded is completely lost

Perhaps just having a different data stream for every major thing, combined later would solve this.

It concerns me that a single error in any part of loading makes the entire thing unloadable (particularly because I've just edited it in #1225 :rofl:)