Bug Fixes:
- When removing a segment from a chain don't try to merge with the previous chain if the previous chain is the removed segment. (this was causing the lockup).
- When a belt entity goes from a visible slot to a non-visible slot or vice versa, queue a visibility change request from the other thread so that we can update its visibility on the main thread (this should fix the "orphaned" entities).
- Fix a couple entity orphaning issue.
- If a delta is refreshed (because one of its neighbors is destroyed) don't orphan its entities.
- chasm structure destruction now happens after collision generation so we can use the same logic to avoid "thin" chasms.
- Streamways no longer try to consume every available processor (be a good citizen). Hoping this is a little better with people running on low core machines.