Game FPS example improved

[octopoulos]

4 improvements:

1. Performance with 300 balls on my computer was sub 1 fps, and after the first commit, it jumped to 60 fps.
   This was achieved by doing 3 things:
   a) move sphereCollisions outside the sphere loop => O(n^3) becomes O(n^2), => getting 20 fps about instead of 1 fps.
   b) change collider.clone().center to collider.center.clone() => getting 40 fps;
   c) use temporary Vector3 instead of cloning them => getting 60+fps.

I changed the number of balls from 20 to 100 by default.

2. Air control: easier to control where to jump and land.

3. Adjust throw power: if you hold the mouse button, it throws the ball with more force.
   Also, if you move, it impacts the throw a bit, so to throw really far, you want to move forward and hold the button for 2 sec or so.

4. Basic collision between player and the balls.

[mrdoob]

Nice!

[mrdoob]

Thanks!