Fixed a bug in LOD boundary behavior

- changed the way we calculate whether or not to render a parent "average" voxel so
  that if any of it's most distant child would not be visible, then it's used instead
  of it's children
- added precalculated value for topFarLeft corner of AABox (optimization)
- changed VoxelSystem::newTreeToArrays() and VoxelTree::encodeTreeBitstreamRecursion()
  to use the same help function for determining this LOD boundary behavior
- deleted old dead code in voxel-server and VoxelTree for picking which node to start
  sending with, since it wasn't being used
- added VoxelNode::furthestDistanceToCamera() which tells you not the distance to the
  center of the voxel, but the distance from the camera to the furthest corner relative
  to the camera.
- added ViewFrustum::getFurthestPointFromCamera() which given an axis-aligned box will
  tell you which vertex of the box is furthest from the camera
- cleaned up some white space
- fixed a compiler warning