* Cache node in voxel area index when possible
The index function according to the MSVC profiler actually takes up a significant time slice (around ~5% of total time for the process) during normal game-play.
Might not be accurate but still good to not recalculate it twice.
* Remove `setNodeNoRef` from VM
* VM: remove old commented out print statement
* Rename IWritableNodeDefManager to NodeDefManager
* Make INodeDefManager functions const
* Use "const *NodeDefManager" instead of "*INodeDefManager"
* Remove unused INodeDefManager class
* Merge NodeDefManager and CNodeDefManager
* Document NodeDefManager
* Code modernization: subfolders
Modernize various code on subfolders client, network, script, threading, unittests, util
* empty function
* default constructor/destructor
* for range-based loops
* use emplace_back instead of push_back
* C++ STL header style
* Make connection.cpp readable in a pointed place + typo
