Performance improvements in the SDL viewer. (#114)
Performance improvements in the SDL viewer. (#114)

- Render less points while moving.
- Never use LOD.
- Choose the level to render on the amount of nodes that fit in the
  cache.
cartographer-project/point_cloud_viewer,cartographer-project/point_cloud_viewer,googlecartographer/point_cloud_viewer,cartographer-project/point_cloud_viewer,googlecartographer/point_cloud_viewer,googlecartographer/point_cloud_viewer,googlecartographer/point_cloud_viewer,cartographer-project/point_cloud_viewer,googlecartographer/point_cloud_viewer,cartographer-project/point_cloud_viewer