Add automatic random splats on timer.

[DavidHaitch]

I wanted to use this sim as a more passive visualization for a party. To support this, I've added an "auto-splat" mode that adds random splats on a configurable interval.

[DavidHaitch]

(Tip: for best results, let the autosplats develop slowly over time, with low density and velocity diffusions.)

[konnermacias]

This looks great! I'm going to try to incorporate these random autosplats with spotify song tempo