[Feature] Kill particles when they go offscreen

[djeedai]

Describe the solution you'd like

Split from #118.

A new KillOffscreenModifier modifier killing particles when the go offscreen.

Describe why you want that solution. Is this related to a problem?

Often visual effects are just that, visual, and simulating particles which are offscreen and not rendered is a waste of GPU resources. In some cases (but not all) the camera is constrained in such a way that once a particle goes offscreen it can't be visible again. Making sure the particle is not simulated in this case is otherwise quite difficult without this modifier.

Describe alternatives you've considered

Use KillAabbModifier for 2D, when the camera cannot rotate. There's no real equivalent for 3D.