changes made to learn from the open source physics codes.

1. made n selectable by defining nmax and insert as the n maximum limit
2. made v0 selectable by changing the codes
3. made arrows array to be drawn to understand where the particles are heading
4. made text array to allow eye balling what each particle is doing
5 change some minor values to make cellSize selectable as well.
6 added e coefficient of restitution but the codes does not work well when e = 0 probably due to the collision detection codes, goes to a deep loop when too much particles are near each other and the model is not too correct as it behaves strangely, the particles all move to one side?

Enjoy!