Blender Git Loki

BGE performance:

- Vast performance increase when removing scene containing large number of
objects: the sensor/controller map was updated for each deleted object,
causing massive slow down when the number of objects was large (O(n^2)).
- Use reference when scanning the sensor map => avoid useless copy.
- Remove dynamically the object bounding box from the DBVT when the object
is invisible => faster culling.