Voxel memory stats/Load voxels on persist thread/Save memory with VoxelNode size savings

- added new stats to client to show actual memory usage by local VoxelTree
- added support for web server inside of voxel server to display stats of current memory usage in voxel server
- load voxels in voxel server on persist thread so that voxel server assignments "start faster"
- better alignment of VoxelNode members to save on memory usage