bug fixes

* Fixes random CPU spike in voxel server after some clients shutdown - fixes #2039 
* Switches Auto-Adjust LOD to use moving average over ~5 seconds - closes #2114 

On the CPU spike - What was happening is that if the NodeList saw our agent go away but we had it locked then it doesn't delete the node data. But since the node no longer exists in the domain list we wouldn't find it by ID and we'd spin out. The fix is to abandon our thread if we haven't been able to find our node by ID after a certain number of attempts.