Version 0.4.1. Performance loss :(

- Added a Bullet reference to the Game scene to reduce the vector
accesses in the game loop.
- Seems like there is a performance loss in general. When activating the
profiler, sometimes the game loads with white background and running at
60 fps. Otherwise, it runs below 60 fps. I've tried to comment the loops
at the Game Loop to see if they are the problem behind the performance,
but doesn't seem to.